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	$247.36	3.815%	$256.7968	$256.80	$256.80	$256.80
Purchase #2	$132.38	13.179%	$149.8264	$149.83	$149.85	$149.80
Purchase #3	$33.72	5.454%	$35.5591	$35.56	$35.55	$35.60
Purchase #4	$203.47	4.259%	$212.1358	$212.14	$212.15	$212.10
Purchase #5	$35.45	6.654%	$37.8088	$37.81	$37.80	$37.80
Purchase #6	$74.83	11.532%	$83.4594	$83.46	$83.45	$83.50
Purchase #7	$120.52	4.552%	$126.0061	$126.01	$126.00	$126.00
7 purchase totals =	$847.73		$901.5924	$901.61	$901.60	$901.60