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	$28.72	11.753%	$32.0955	$32.10	$32.10	$32.10
Purchase #2	$226.47	13.135%	$256.2168	$256.22	$256.20	$256.20
Purchase #3	$247.43	7.298%	$265.4874	$265.49	$265.50	$265.50
Purchase #4	$197.98	3.146%	$204.2085	$204.21	$204.20	$204.20
Purchase #5	$195.26	7.326%	$209.5647	$209.56	$209.55	$209.60
Purchase #6	$93.81	12.366%	$105.4105	$105.41	$105.40	$105.40
Purchase #7	$67.38	7.504%	$72.4362	$72.44	$72.45	$72.40
7 purchase totals =	$1,057.05		$1,145.4196	$1,145.43	$1,145.40	$1,145.40