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	$238.86	7.315%	$256.3326	$256.33	$256.35	$256.30
Purchase #2	$187.82	5.862%	$198.83	$198.83	$198.85	$198.80
Purchase #3	$242.30	11.490%	$270.1403	$270.14	$270.15	$270.10
Purchase #4	$88.59	4.272%	$92.3746	$92.37	$92.35	$92.40
Purchase #5	$7.29	10.503%	$8.0557	$8.06	$8.05	$8.10
Purchase #6	$112.85	11.780%	$126.1437	$126.14	$126.15	$126.10
Purchase #7	$39.83	11.203%	$44.2922	$44.29	$44.30	$44.30
7 purchase totals =	$917.54		$996.1691	$996.16	$996.20	$996.10