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	$222.29	4.780%	$232.9155	$232.92	$232.90	$232.90
Purchase #2	$89.39	12.353%	$100.4323	$100.43	$100.45	$100.40
Purchase #3	$144.53	12.298%	$162.3043	$162.30	$162.30	$162.30
Purchase #4	$19.39	3.502%	$20.069	$20.07	$20.05	$20.10
Purchase #5	$43.29	11.341%	$48.1995	$48.20	$48.20	$48.20
Purchase #6	$131.59	10.195%	$145.0056	$145.01	$145.00	$145.00
Purchase #7	$33.47	8.708%	$36.3846	$36.38	$36.40	$36.40
7 purchase totals =	$683.95		$745.3108	$745.31	$745.30	$745.30