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	$129.84	7.600%	$139.7078	$139.71	$139.70	$139.70
Purchase #2	$144.40	5.134%	$151.8135	$151.81	$151.80	$151.80
Purchase #3	$33.63	11.118%	$37.369	$37.37	$37.35	$37.40
Purchase #4	$225.84	13.595%	$256.5429	$256.54	$256.55	$256.50
Purchase #5	$206.66	6.358%	$219.7994	$219.80	$219.80	$219.80
Purchase #6	$92.90	13.508%	$105.4489	$105.45	$105.45	$105.40
Purchase #7	$73.80	11.156%	$82.0331	$82.03	$82.05	$82.00
7 purchase totals =	$907.07		$992.7146	$992.71	$992.70	$992.60