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	$64.76	12.126%	$72.6128	$72.61	$72.60	$72.60
Purchase #2	$239.74	13.578%	$272.2919	$272.29	$272.30	$272.30
Purchase #3	$114.44	10.584%	$126.5523	$126.55	$126.55	$126.60
Purchase #4	$41.46	6.131%	$44.0019	$44.00	$44.00	$44.00
Purchase #5	$36.51	10.847%	$40.4702	$40.47	$40.45	$40.50
Purchase #6	$213.67	8.331%	$231.4708	$231.47	$231.45	$231.50
Purchase #7	$209.37	10.777%	$231.9338	$231.93	$231.95	$231.90
7 purchase totals =	$919.95		$1,019.3337	$1,019.32	$1,019.30	$1,019.40