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	$19.27	9.547%	$21.1097	$21.11	$21.10	$21.10
Purchase #2	$236.77	5.817%	$250.5429	$250.54	$250.55	$250.50
Purchase #3	$134.53	9.375%	$147.1422	$147.14	$147.15	$147.10
Purchase #4	$105.61	12.450%	$118.7584	$118.76	$118.75	$118.80
Purchase #5	$18.54	12.153%	$20.7932	$20.79	$20.80	$20.80
Purchase #6	$211.38	5.700%	$223.4287	$223.43	$223.45	$223.40
Purchase #7	$247.97	3.163%	$255.8133	$255.81	$255.80	$255.80
7 purchase totals =	$974.07		$1,037.5884	$1,037.58	$1,037.60	$1,037.50