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	$227.82	7.126%	$244.0545	$244.05	$244.05	$244.10
Purchase #2	$223.37	6.272%	$237.3798	$237.38	$237.40	$237.40
Purchase #3	$245.57	5.133%	$258.1751	$258.18	$258.20	$258.20
Purchase #4	$173.49	9.699%	$190.3168	$190.32	$190.30	$190.30
Purchase #5	$45.90	10.436%	$50.6901	$50.69	$50.70	$50.70
Purchase #6	$40.87	12.353%	$45.9187	$45.92	$45.90	$45.90
Purchase #7	$166.34	13.222%	$188.3335	$188.33	$188.35	$188.30
7 purchase totals =	$1,123.36		$1,214.8685	$1,214.87	$1,214.90	$1,214.90