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	$41.89	7.793%	$45.1545	$45.15	$45.15	$45.20
Purchase #2	$59.31	8.312%	$64.2398	$64.24	$64.25	$64.20
Purchase #3	$188.39	12.695%	$212.3061	$212.31	$212.30	$212.30
Purchase #4	$211.29	3.143%	$217.9308	$217.93	$217.95	$217.90
Purchase #5	$239.98	4.488%	$250.7503	$250.75	$250.75	$250.80
Purchase #6	$124.32	10.772%	$137.7118	$137.71	$137.70	$137.70
Purchase #7	$58.57	11.678%	$65.4098	$65.41	$65.40	$65.40
7 purchase totals =	$923.75		$993.5031	$993.50	$993.50	$993.50