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	$108.91	13.745%	$123.8797	$123.88	$123.90	$123.90
Purchase #2	$40.83	8.320%	$44.2271	$44.23	$44.25	$44.20
Purchase #3	$203.34	12.677%	$229.1174	$229.12	$229.10	$229.10
Purchase #4	$237.26	12.209%	$266.2271	$266.23	$266.25	$266.20
Purchase #5	$137.29	10.819%	$152.1434	$152.14	$152.15	$152.10
Purchase #6	$84.40	6.580%	$89.9535	$89.95	$89.95	$90.00
Purchase #7	$33.27	4.735%	$34.8453	$34.85	$34.85	$34.80
7 purchase totals =	$845.30		$940.3935	$940.40	$940.45	$940.30