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	$129.43	7.333%	$138.9211	$138.92	$138.90	$138.90
Purchase #2	$162.41	13.331%	$184.0609	$184.06	$184.05	$184.10
Purchase #3	$115.58	13.138%	$130.7649	$130.76	$130.75	$130.80
Purchase #4	$75.61	9.108%	$82.4966	$82.50	$82.50	$82.50
Purchase #5	$48.52	9.676%	$53.2148	$53.21	$53.20	$53.20
Purchase #6	$216.35	3.471%	$223.8595	$223.86	$223.85	$223.90
Purchase #7	$100.57	4.628%	$105.2244	$105.22	$105.20	$105.20
7 purchase totals =	$848.47		$918.5422	$918.53	$918.45	$918.60