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	$124.33	10.232%	$137.0514	$137.05	$137.05	$137.10
Purchase #2	$240.74	3.489%	$249.1394	$249.14	$249.15	$249.10
Purchase #3	$216.58	3.204%	$223.5192	$223.52	$223.50	$223.50
Purchase #4	$164.39	6.129%	$174.4655	$174.47	$174.45	$174.50
Purchase #5	$94.45	6.792%	$100.865	$100.87	$100.85	$100.90
Purchase #6	$62.85	11.352%	$69.9847	$69.98	$70.00	$70.00
Purchase #7	$13.43	12.653%	$15.1293	$15.13	$15.15	$15.10
7 purchase totals =	$916.77		$970.1545	$970.16	$970.15	$970.20