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	$163.35	6.238%	$173.5398	$173.54	$173.55	$173.50
Purchase #2	$89.32	11.300%	$99.4132	$99.41	$99.40	$99.40
Purchase #3	$89.59	12.647%	$100.9204	$100.92	$100.90	$100.90
Purchase #4	$87.84	11.673%	$98.0936	$98.09	$98.10	$98.10
Purchase #5	$197.34	12.621%	$222.2463	$222.25	$222.25	$222.20
Purchase #6	$36.67	11.675%	$40.9512	$40.95	$40.95	$41.00
Purchase #7	$80.29	6.680%	$85.6534	$85.65	$85.65	$85.70
7 purchase totals =	$744.40		$820.8179	$820.81	$820.80	$820.80