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	$50.77	8.787%	$55.2312	$55.23	$55.25	$55.20
Purchase #2	$220.56	3.511%	$228.3039	$228.30	$228.30	$228.30
Purchase #3	$18.52	11.325%	$20.6174	$20.62	$20.60	$20.60
Purchase #4	$82.84	6.798%	$88.4715	$88.47	$88.45	$88.50
Purchase #5	$75.33	13.549%	$85.5365	$85.54	$85.55	$85.50
Purchase #6	$126.76	8.612%	$137.6766	$137.68	$137.70	$137.70
Purchase #7	$125.73	4.302%	$131.1389	$131.14	$131.15	$131.10
7 purchase totals =	$700.51		$746.9760	$746.98	$747.00	$746.90