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	$66.48	7.262%	$71.3078	$71.31	$71.30	$71.30
Purchase #2	$78.88	11.754%	$88.1516	$88.15	$88.15	$88.20
Purchase #3	$54.42	13.782%	$61.9202	$61.92	$61.90	$61.90
Purchase #4	$152.41	13.319%	$172.7095	$172.71	$172.70	$172.70
Purchase #5	$116.70	8.392%	$126.4935	$126.49	$126.50	$126.50
Purchase #6	$116.27	10.148%	$128.0691	$128.07	$128.05	$128.10
Purchase #7	$195.89	5.208%	$206.092	$206.09	$206.10	$206.10
7 purchase totals =	$781.05		$854.7437	$854.74	$854.70	$854.80