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	$98.95	12.375%	$111.1951	$111.20	$111.20	$111.20
Purchase #2	$243.48	7.582%	$261.9407	$261.94	$261.95	$261.90
Purchase #3	$158.99	8.381%	$172.315	$172.32	$172.30	$172.30
Purchase #4	$99.78	4.434%	$104.2042	$104.20	$104.20	$104.20
Purchase #5	$244.93	13.311%	$277.5326	$277.53	$277.55	$277.50
Purchase #6	$176.49	12.497%	$198.546	$198.55	$198.55	$198.50
Purchase #7	$138.80	10.666%	$153.6044	$153.60	$153.60	$153.60
7 purchase totals =	$1,161.42		$1,279.3380	$1,279.34	$1,279.35	$1,279.20