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	$200.96	10.338%	$221.7352	$221.74	$221.75	$221.70
Purchase #2	$100.44	12.682%	$113.1778	$113.18	$113.20	$113.20
Purchase #3	$136.55	3.340%	$141.1108	$141.11	$141.10	$141.10
Purchase #4	$246.54	10.379%	$272.1284	$272.13	$272.15	$272.10
Purchase #5	$161.93	8.546%	$175.7685	$175.77	$175.75	$175.80
Purchase #6	$77.39	10.444%	$85.4726	$85.47	$85.45	$85.50
Purchase #7	$78.85	7.823%	$85.0184	$85.02	$85.00	$85.00
7 purchase totals =	$1,002.66		$1,094.4117	$1,094.42	$1,094.40	$1,094.40