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	$45.53	10.667%	$50.3867	$50.39	$50.40	$50.40
Purchase #2	$83.44	9.760%	$91.5837	$91.58	$91.60	$91.60
Purchase #3	$64.51	12.214%	$72.3893	$72.39	$72.40	$72.40
Purchase #4	$59.78	3.524%	$61.8866	$61.89	$61.90	$61.90
Purchase #5	$137.26	8.654%	$149.1385	$149.14	$149.15	$149.10
Purchase #6	$41.29	6.834%	$44.1118	$44.11	$44.10	$44.10
Purchase #7	$101.47	4.190%	$105.7216	$105.72	$105.70	$105.70
7 purchase totals =	$533.28		$575.2182	$575.22	$575.25	$575.20