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	$39.83	6.287%	$42.3341	$42.33	$42.35	$42.30
Purchase #2	$22.25	4.168%	$23.1774	$23.18	$23.20	$23.20
Purchase #3	$214.94	9.298%	$234.9251	$234.93	$234.95	$234.90
Purchase #4	$194.34	7.453%	$208.8242	$208.82	$208.80	$208.80
Purchase #5	$244.70	4.497%	$255.7042	$255.70	$255.70	$255.70
Purchase #6	$53.64	11.459%	$59.7866	$59.79	$59.80	$59.80
Purchase #7	$112.45	9.502%	$123.135	$123.14	$123.15	$123.10
7 purchase totals =	$882.15		$947.8866	$947.89	$947.95	$947.80