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	$38.82	4.278%	$40.4807	$40.48	$40.50	$40.50
Purchase #2	$56.71	8.171%	$61.3438	$61.34	$61.35	$61.30
Purchase #3	$149.74	9.694%	$164.2558	$164.26	$164.25	$164.30
Purchase #4	$12.34	11.866%	$13.8043	$13.80	$13.80	$13.80
Purchase #5	$210.57	10.249%	$232.1513	$232.15	$232.15	$232.20
Purchase #6	$202.59	11.244%	$225.3692	$225.37	$225.35	$225.40
Purchase #7	$236.27	12.548%	$265.9172	$265.92	$265.90	$265.90
7 purchase totals =	$907.04		$1,003.3223	$1,003.32	$1,003.30	$1,003.40