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	$33.39	13.465%	$37.886	$37.89	$37.90	$37.90
Purchase #2	$128.71	3.743%	$133.5276	$133.53	$133.55	$133.50
Purchase #3	$94.29	5.170%	$99.1648	$99.16	$99.15	$99.20
Purchase #4	$214.37	7.684%	$230.8422	$230.84	$230.85	$230.80
Purchase #5	$39.96	3.754%	$41.4601	$41.46	$41.45	$41.50
Purchase #6	$198.81	6.753%	$212.2356	$212.24	$212.25	$212.20
Purchase #7	$246.34	11.114%	$273.7182	$273.72	$273.70	$273.70
7 purchase totals =	$955.87		$1,028.8345	$1,028.84	$1,028.85	$1,028.80