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	$219.49	5.298%	$231.1186	$231.12	$231.10	$231.10
Purchase #2	$42.39	8.275%	$45.8978	$45.90	$45.90	$45.90
Purchase #3	$60.90	12.676%	$68.6197	$68.62	$68.60	$68.60
Purchase #4	$137.36	9.549%	$150.4765	$150.48	$150.50	$150.50
Purchase #5	$108.57	7.164%	$116.348	$116.35	$116.35	$116.30
Purchase #6	$140.40	13.816%	$159.7977	$159.80	$159.80	$159.80
Purchase #7	$29.70	11.613%	$33.1491	$33.15	$33.15	$33.10
7 purchase totals =	$738.81		$805.4074	$805.42	$805.40	$805.30