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	$125.90	12.146%	$141.1918	$141.19	$141.20	$141.20
Purchase #2	$237.77	9.570%	$260.5246	$260.52	$260.50	$260.50
Purchase #3	$140.90	7.764%	$151.8395	$151.84	$151.85	$151.80
Purchase #4	$22.91	8.143%	$24.7756	$24.78	$24.80	$24.80
Purchase #5	$153.61	5.728%	$162.4088	$162.41	$162.40	$162.40
Purchase #6	$93.58	12.573%	$105.3458	$105.35	$105.35	$105.30
Purchase #7	$33.50	12.212%	$37.591	$37.59	$37.60	$37.60
7 purchase totals =	$808.17		$883.6771	$883.68	$883.70	$883.60