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	$127.91	7.654%	$137.7002	$137.70	$137.70	$137.70
Purchase #2	$150.81	13.142%	$170.6295	$170.63	$170.65	$170.60
Purchase #3	$6.58	8.617%	$7.147	$7.15	$7.15	$7.10
Purchase #4	$136.31	10.508%	$150.6335	$150.63	$150.65	$150.60
Purchase #5	$97.96	13.809%	$111.4873	$111.49	$111.50	$111.50
Purchase #6	$164.49	7.596%	$176.9847	$176.98	$177.00	$177.00
Purchase #7	$94.26	6.799%	$100.6687	$100.67	$100.65	$100.70
7 purchase totals =	$778.32		$855.2509	$855.25	$855.30	$855.20