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	$222.46	12.602%	$250.4944	$250.49	$250.50	$250.50
Purchase #2	$137.97	12.593%	$155.3446	$155.34	$155.35	$155.30
Purchase #3	$53.32	4.639%	$55.7935	$55.79	$55.80	$55.80
Purchase #4	$66.72	11.238%	$74.218	$74.22	$74.20	$74.20
Purchase #5	$76.48	3.245%	$78.9618	$78.96	$78.95	$79.00
Purchase #6	$63.49	5.864%	$67.2131	$67.21	$67.20	$67.20
Purchase #7	$22.45	3.588%	$23.2555	$23.26	$23.25	$23.30
7 purchase totals =	$642.89		$705.2809	$705.27	$705.25	$705.30