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	$82.32	9.828%	$90.4104	$90.41	$90.40	$90.40
Purchase #2	$130.83	5.594%	$138.1486	$138.15	$138.15	$138.10
Purchase #3	$241.84	8.539%	$262.4907	$262.49	$262.50	$262.50
Purchase #4	$10.28	13.229%	$11.6399	$11.64	$11.65	$11.60
Purchase #5	$61.57	9.743%	$67.5688	$67.57	$67.55	$67.60
Purchase #6	$44.77	12.158%	$50.2131	$50.21	$50.20	$50.20
Purchase #7	$150.69	5.843%	$159.4948	$159.49	$159.50	$159.50
7 purchase totals =	$722.30		$779.9663	$779.96	$779.95	$779.90