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	$42.59	9.308%	$46.5543	$46.55	$46.55	$46.60
Purchase #2	$40.80	8.371%	$44.2154	$44.22	$44.20	$44.20
Purchase #3	$114.89	12.180%	$128.8836	$128.88	$128.90	$128.90
Purchase #4	$45.27	6.261%	$48.1044	$48.10	$48.10	$48.10
Purchase #5	$157.71	7.651%	$169.7764	$169.78	$169.80	$169.80
Purchase #6	$37.47	12.378%	$42.108	$42.11	$42.10	$42.10
Purchase #7	$146.46	6.453%	$155.9111	$155.91	$155.90	$155.90
7 purchase totals =	$585.19		$635.5532	$635.55	$635.55	$635.60