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	$249.80	13.413%	$283.3057	$283.31	$283.30	$283.30
Purchase #2	$189.27	5.504%	$199.6874	$199.69	$199.70	$199.70
Purchase #3	$49.56	7.562%	$53.3077	$53.31	$53.30	$53.30
Purchase #4	$188.34	5.680%	$199.0377	$199.04	$199.05	$199.00
Purchase #5	$127.79	7.328%	$137.1545	$137.15	$137.15	$137.20
Purchase #6	$74.47	5.533%	$78.5904	$78.59	$78.60	$78.60
Purchase #7	$237.93	11.315%	$264.8518	$264.85	$264.85	$264.90
7 purchase totals =	$1,117.16		$1,215.9352	$1,215.94	$1,215.95	$1,216.00