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	$34.54	5.259%	$36.3565	$36.36	$36.35	$36.40
Purchase #2	$61.48	10.359%	$67.8487	$67.85	$67.85	$67.80
Purchase #3	$95.69	4.543%	$100.0372	$100.04	$100.05	$100.00
Purchase #4	$26.79	3.144%	$27.6323	$27.63	$27.65	$27.60
Purchase #5	$116.82	13.601%	$132.7087	$132.71	$132.70	$132.70
Purchase #6	$130.28	8.349%	$141.1571	$141.16	$141.15	$141.20
Purchase #7	$152.56	3.457%	$157.834	$157.83	$157.85	$157.80
7 purchase totals =	$618.16		$663.5745	$663.58	$663.60	$663.50