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	$145.54	6.782%	$155.4105	$155.41	$155.40	$155.40
Purchase #2	$65.38	10.778%	$72.4267	$72.43	$72.45	$72.40
Purchase #3	$20.35	8.371%	$22.0535	$22.05	$22.05	$22.10
Purchase #4	$226.65	9.329%	$247.7942	$247.79	$247.80	$247.80
Purchase #5	$130.79	8.487%	$141.8901	$141.89	$141.90	$141.90
Purchase #6	$115.70	7.121%	$123.939	$123.94	$123.95	$123.90
Purchase #7	$75.81	7.344%	$81.3775	$81.38	$81.40	$81.40
7 purchase totals =	$780.22		$844.8915	$844.89	$844.95	$844.90