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	$50.86	12.676%	$57.307	$57.31	$57.30	$57.30
Purchase #2	$45.25	10.716%	$50.099	$50.10	$50.10	$50.10
Purchase #3	$10.71	9.550%	$11.7328	$11.73	$11.75	$11.70
Purchase #4	$30.30	8.220%	$32.7907	$32.79	$32.80	$32.80
Purchase #5	$170.57	5.830%	$180.5142	$180.51	$180.50	$180.50
Purchase #6	$86.30	8.148%	$93.3317	$93.33	$93.35	$93.30
Purchase #7	$48.90	9.324%	$53.4594	$53.46	$53.45	$53.50
7 purchase totals =	$442.89		$479.2348	$479.23	$479.25	$479.20