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	$25.33	11.797%	$28.3182	$28.32	$28.30	$28.30
Purchase #2	$247.35	13.187%	$279.968	$279.97	$279.95	$280.00
Purchase #3	$31.50	4.519%	$32.9235	$32.92	$32.90	$32.90
Purchase #4	$140.89	3.677%	$146.0705	$146.07	$146.05	$146.10
Purchase #5	$180.82	8.804%	$196.7394	$196.74	$196.75	$196.70
Purchase #6	$194.81	4.369%	$203.3212	$203.32	$203.30	$203.30
Purchase #7	$236.95	6.846%	$253.1716	$253.17	$253.15	$253.20
7 purchase totals =	$1,057.65		$1,140.5124	$1,140.51	$1,140.40	$1,140.50