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	$135.29	9.111%	$147.6163	$147.62	$147.60	$147.60
Purchase #2	$101.97	6.756%	$108.8591	$108.86	$108.85	$108.90
Purchase #3	$36.84	12.427%	$41.4181	$41.42	$41.40	$41.40
Purchase #4	$185.85	7.424%	$199.6475	$199.65	$199.65	$199.60
Purchase #5	$37.34	7.536%	$40.1539	$40.15	$40.15	$40.20
Purchase #6	$85.73	5.204%	$90.1914	$90.19	$90.20	$90.20
Purchase #7	$114.55	5.213%	$120.5215	$120.52	$120.50	$120.50
7 purchase totals =	$697.57		$748.4078	$748.41	$748.35	$748.40