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	$107.89	13.695%	$122.6655	$122.67	$122.65	$122.70
Purchase #2	$66.34	9.368%	$72.5547	$72.55	$72.55	$72.60
Purchase #3	$37.50	5.821%	$39.6829	$39.68	$39.70	$39.70
Purchase #4	$101.98	9.392%	$111.558	$111.56	$111.55	$111.60
Purchase #5	$166.36	7.443%	$178.7422	$178.74	$178.75	$178.70
Purchase #6	$95.64	7.810%	$103.1095	$103.11	$103.10	$103.10
Purchase #7	$36.45	5.546%	$38.4715	$38.47	$38.45	$38.50
7 purchase totals =	$612.16		$666.7843	$666.78	$666.75	$666.90