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	$11.62	3.769%	$12.058	$12.06	$12.05	$12.10
Purchase #2	$39.37	8.369%	$42.6649	$42.66	$42.65	$42.70
Purchase #3	$87.37	10.525%	$96.5657	$96.57	$96.55	$96.60
Purchase #4	$209.52	5.761%	$221.5904	$221.59	$221.60	$221.60
Purchase #5	$74.51	4.276%	$77.696	$77.70	$77.70	$77.70
Purchase #6	$75.43	13.140%	$85.3415	$85.34	$85.35	$85.30
Purchase #7	$123.74	10.651%	$136.9195	$136.92	$136.90	$136.90
7 purchase totals =	$621.56		$672.8360	$672.84	$672.80	$672.90