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	$130.40	5.172%	$137.1443	$137.14	$137.15	$137.10
Purchase #2	$108.43	9.443%	$118.669	$118.67	$118.65	$118.70
Purchase #3	$201.84	10.547%	$223.1281	$223.13	$223.15	$223.10
Purchase #4	$212.69	6.178%	$225.83	$225.83	$225.85	$225.80
Purchase #5	$140.45	11.187%	$156.1621	$156.16	$156.15	$156.20
Purchase #6	$128.38	7.129%	$137.5322	$137.53	$137.55	$137.50
Purchase #7	$231.83	7.764%	$249.8293	$249.83	$249.85	$249.80
7 purchase totals =	$1,154.02		$1,248.2950	$1,248.29	$1,248.35	$1,248.20