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	$37.96	11.463%	$42.3114	$42.31	$42.30	$42.30
Purchase #2	$146.86	12.400%	$165.0706	$165.07	$165.05	$165.10
Purchase #3	$54.67	7.713%	$58.8867	$58.89	$58.90	$58.90
Purchase #4	$164.62	8.644%	$178.8498	$178.85	$178.85	$178.80
Purchase #5	$85.25	13.424%	$96.694	$96.69	$96.70	$96.70
Purchase #6	$135.87	12.142%	$152.3673	$152.37	$152.35	$152.40
Purchase #7	$22.71	11.732%	$25.3743	$25.37	$25.35	$25.40
7 purchase totals =	$647.94		$719.5541	$719.55	$719.50	$719.60