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	$99.78	9.503%	$109.2621	$109.26	$109.25	$109.30
Purchase #2	$116.34	5.675%	$122.9423	$122.94	$122.95	$122.90
Purchase #3	$247.60	8.766%	$269.3046	$269.30	$269.30	$269.30
Purchase #4	$63.43	12.314%	$71.2408	$71.24	$71.25	$71.20
Purchase #5	$74.79	4.483%	$78.1428	$78.14	$78.15	$78.10
Purchase #6	$141.61	7.716%	$152.5366	$152.54	$152.55	$152.50
Purchase #7	$187.39	3.741%	$194.4003	$194.40	$194.40	$194.40
7 purchase totals =	$930.94		$997.8295	$997.82	$997.85	$997.70