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	$240.28	7.281%	$257.7748	$257.77	$257.75	$257.80
Purchase #2	$95.75	4.494%	$100.053	$100.05	$100.05	$100.10
Purchase #3	$172.42	5.290%	$181.541	$181.54	$181.55	$181.50
Purchase #4	$65.33	9.330%	$71.4253	$71.43	$71.45	$71.40
Purchase #5	$6.54	8.712%	$7.1098	$7.11	$7.10	$7.10
Purchase #6	$141.33	12.725%	$159.3142	$159.31	$159.30	$159.30
Purchase #7	$159.31	12.142%	$178.6534	$178.65	$178.65	$178.70
7 purchase totals =	$880.96		$955.8715	$955.86	$955.85	$955.90