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	$37.42	9.320%	$40.9075	$40.91	$40.90	$40.90
Purchase #2	$37.39	13.727%	$42.5225	$42.52	$42.50	$42.50
Purchase #3	$124.76	12.368%	$140.1903	$140.19	$140.20	$140.20
Purchase #4	$126.42	11.761%	$141.2883	$141.29	$141.30	$141.30
Purchase #5	$55.52	3.579%	$57.5071	$57.51	$57.50	$57.50
Purchase #6	$26.36	11.807%	$29.4723	$29.47	$29.45	$29.50
Purchase #7	$209.38	10.700%	$231.7837	$231.78	$231.80	$231.80
7 purchase totals =	$617.25		$683.6717	$683.67	$683.65	$683.70