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	$48.67	11.429%	$54.2325	$54.23	$54.25	$54.20
Purchase #2	$75.94	9.485%	$83.1429	$83.14	$83.15	$83.10
Purchase #3	$119.72	9.834%	$131.4933	$131.49	$131.50	$131.50
Purchase #4	$59.89	11.429%	$66.7348	$66.73	$66.75	$66.70
Purchase #5	$203.37	4.619%	$212.7637	$212.76	$212.75	$212.80
Purchase #6	$62.96	3.240%	$64.9999	$65.00	$65.00	$65.00
Purchase #7	$168.29	11.412%	$187.4953	$187.50	$187.50	$187.50
7 purchase totals =	$738.84		$800.8624	$800.85	$800.90	$800.80