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	$48.25	5.391%	$50.8512	$50.85	$50.85	$50.90
Purchase #2	$83.75	9.708%	$91.8805	$91.88	$91.90	$91.90
Purchase #3	$230.27	3.669%	$238.7186	$238.72	$238.70	$238.70
Purchase #4	$162.38	10.573%	$179.5484	$179.55	$179.55	$179.50
Purchase #5	$48.44	3.563%	$50.1659	$50.17	$50.15	$50.20
Purchase #6	$86.71	4.208%	$90.3588	$90.36	$90.35	$90.40
Purchase #7	$247.40	13.125%	$279.8713	$279.87	$279.85	$279.90
7 purchase totals =	$907.20		$981.3947	$981.40	$981.35	$981.50