Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$250.55	9.564%	$274.5126	$274.51	$274.50	$274.50
Purchase #2	$190.86	6.405%	$203.0846	$203.08	$203.10	$203.10
Purchase #3	$220.88	6.293%	$234.78	$234.78	$234.80	$234.80
Purchase #4	$106.74	4.599%	$111.649	$111.65	$111.65	$111.60
Purchase #5	$91.84	8.379%	$99.5353	$99.54	$99.55	$99.50
Purchase #6	$192.64	10.515%	$212.8961	$212.90	$212.90	$212.90
Purchase #7	$144.49	4.102%	$150.417	$150.42	$150.40	$150.40
7 purchase totals =	$1,198.00		$1,286.8746	$1,286.88	$1,286.90	$1,286.80