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	$45.65	10.817%	$50.588	$50.59	$50.60	$50.60
Purchase #2	$110.27	5.690%	$116.5444	$116.54	$116.55	$116.50
Purchase #3	$212.58	5.820%	$224.9522	$224.95	$224.95	$225.00
Purchase #4	$87.26	6.541%	$92.9677	$92.97	$92.95	$93.00
Purchase #5	$111.91	11.801%	$125.1165	$125.12	$125.10	$125.10
Purchase #6	$83.47	7.255%	$89.5257	$89.53	$89.55	$89.50
Purchase #7	$151.39	13.828%	$172.3242	$172.32	$172.30	$172.30
7 purchase totals =	$802.53		$872.0187	$872.02	$872.00	$872.00