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	$35.34	12.753%	$39.8469	$39.85	$39.85	$39.80
Purchase #2	$59.55	8.406%	$64.5558	$64.56	$64.55	$64.60
Purchase #3	$196.51	13.729%	$223.4889	$223.49	$223.50	$223.50
Purchase #4	$114.45	7.114%	$122.592	$122.59	$122.60	$122.60
Purchase #5	$72.95	12.541%	$82.0987	$82.10	$82.10	$82.10
Purchase #6	$107.82	9.267%	$117.8117	$117.81	$117.80	$117.80
Purchase #7	$89.36	11.487%	$99.6248	$99.62	$99.60	$99.60
7 purchase totals =	$675.98		$750.0188	$750.02	$750.00	$750.00