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	$96.39	4.281%	$100.5165	$100.52	$100.50	$100.50
Purchase #2	$115.29	8.691%	$125.3099	$125.31	$125.30	$125.30
Purchase #3	$111.37	11.743%	$124.4482	$124.45	$124.45	$124.40
Purchase #4	$211.52	8.600%	$229.7107	$229.71	$229.70	$229.70
Purchase #5	$100.58	4.430%	$105.0357	$105.04	$105.05	$105.00
Purchase #6	$17.88	13.763%	$20.3408	$20.34	$20.35	$20.30
Purchase #7	$55.57	13.576%	$63.1142	$63.11	$63.10	$63.10
7 purchase totals =	$708.60		$768.4760	$768.48	$768.45	$768.30