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	$50.86	13.481%	$57.7164	$57.72	$57.70	$57.70
Purchase #2	$240.53	9.851%	$264.2246	$264.22	$264.20	$264.20
Purchase #3	$152.80	13.554%	$173.5105	$173.51	$173.50	$173.50
Purchase #4	$83.80	12.495%	$94.2708	$94.27	$94.25	$94.30
Purchase #5	$229.65	11.653%	$256.4111	$256.41	$256.40	$256.40
Purchase #6	$21.33	12.691%	$24.037	$24.04	$24.05	$24.00
Purchase #7	$61.41	5.510%	$64.7937	$64.79	$64.80	$64.80
7 purchase totals =	$840.38		$934.9641	$934.96	$934.90	$934.90