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	$115.51	13.317%	$130.8925	$130.89	$130.90	$130.90
Purchase #2	$18.91	9.401%	$20.6877	$20.69	$20.70	$20.70
Purchase #3	$62.60	10.562%	$69.2118	$69.21	$69.20	$69.20
Purchase #4	$42.75	13.202%	$48.3939	$48.39	$48.40	$48.40
Purchase #5	$37.48	5.270%	$39.4552	$39.46	$39.45	$39.50
Purchase #6	$136.33	11.251%	$151.6685	$151.67	$151.65	$151.70
Purchase #7	$92.31	8.695%	$100.3364	$100.34	$100.35	$100.30
7 purchase totals =	$505.89		$560.6460	$560.65	$560.65	$560.70