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	$38.34	3.301%	$39.6056	$39.61	$39.60	$39.60
Purchase #2	$141.86	5.573%	$149.7659	$149.77	$149.75	$149.80
Purchase #3	$78.41	5.184%	$82.4748	$82.47	$82.45	$82.50
Purchase #4	$243.88	5.245%	$256.6715	$256.67	$256.65	$256.70
Purchase #5	$111.95	4.507%	$116.9956	$117.00	$117.00	$117.00
Purchase #6	$165.42	4.295%	$172.5248	$172.52	$172.50	$172.50
Purchase #7	$132.94	4.790%	$139.3078	$139.31	$139.30	$139.30
7 purchase totals =	$912.80		$957.3460	$957.35	$957.25	$957.40