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	$42.56	7.757%	$45.8614	$45.86	$45.85	$45.90
Purchase #2	$160.34	13.258%	$181.5979	$181.60	$181.60	$181.60
Purchase #3	$116.49	6.597%	$124.1748	$124.17	$124.15	$124.20
Purchase #4	$42.57	4.620%	$44.5367	$44.54	$44.55	$44.50
Purchase #5	$40.98	4.599%	$42.8647	$42.86	$42.85	$42.90
Purchase #6	$66.49	4.214%	$69.2919	$69.29	$69.30	$69.30
Purchase #7	$21.50	4.120%	$22.3858	$22.39	$22.40	$22.40
7 purchase totals =	$490.93		$530.7132	$530.71	$530.70	$530.80