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	$108.32	12.304%	$121.6477	$121.65	$121.65	$121.60
Purchase #2	$70.40	10.619%	$77.8758	$77.88	$77.90	$77.90
Purchase #3	$205.41	8.272%	$222.4015	$222.40	$222.40	$222.40
Purchase #4	$148.44	11.503%	$165.5151	$165.52	$165.50	$165.50
Purchase #5	$184.41	7.694%	$198.5985	$198.60	$198.60	$198.60
Purchase #6	$48.93	11.461%	$54.5379	$54.54	$54.55	$54.50
Purchase #7	$123.41	11.127%	$137.1418	$137.14	$137.15	$137.10
7 purchase totals =	$889.32		$977.7183	$977.73	$977.75	$977.60