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	$67.94	6.764%	$72.5355	$72.54	$72.55	$72.50
Purchase #2	$99.39	5.391%	$104.7481	$104.75	$104.75	$104.70
Purchase #3	$177.66	7.795%	$191.5086	$191.51	$191.50	$191.50
Purchase #4	$129.61	8.277%	$140.3378	$140.34	$140.35	$140.30
Purchase #5	$242.31	9.240%	$264.6994	$264.70	$264.70	$264.70
Purchase #6	$95.37	8.724%	$103.6901	$103.69	$103.70	$103.70
Purchase #7	$46.82	13.400%	$53.0939	$53.09	$53.10	$53.10
7 purchase totals =	$859.10		$930.6134	$930.62	$930.65	$930.50