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	$106.34	4.506%	$111.1317	$111.13	$111.15	$111.10
Purchase #2	$237.86	7.824%	$256.4702	$256.47	$256.45	$256.50
Purchase #3	$191.39	6.617%	$204.0543	$204.05	$204.05	$204.10
Purchase #4	$184.37	11.483%	$205.5412	$205.54	$205.55	$205.50
Purchase #5	$246.67	10.516%	$272.6098	$272.61	$272.60	$272.60
Purchase #6	$191.76	11.333%	$213.4922	$213.49	$213.50	$213.50
Purchase #7	$223.92	8.628%	$243.2398	$243.24	$243.25	$243.20
7 purchase totals =	$1,382.31		$1,506.5392	$1,506.53	$1,506.55	$1,506.50