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	$15.55	8.410%	$16.8578	$16.86	$16.85	$16.90
Purchase #2	$241.46	13.742%	$274.6414	$274.64	$274.65	$274.60
Purchase #3	$204.29	11.439%	$227.6587	$227.66	$227.65	$227.70
Purchase #4	$72.80	7.162%	$78.0139	$78.01	$78.00	$78.00
Purchase #5	$73.72	11.709%	$82.3519	$82.35	$82.35	$82.40
Purchase #6	$173.80	4.645%	$181.873	$181.87	$181.85	$181.90
Purchase #7	$239.39	11.630%	$267.2311	$267.23	$267.25	$267.20
7 purchase totals =	$1,021.01		$1,128.6278	$1,128.62	$1,128.60	$1,128.70