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	$127.89	6.382%	$136.0519	$136.05	$136.05	$136.10
Purchase #2	$154.47	5.265%	$162.6028	$162.60	$162.60	$162.60
Purchase #3	$246.75	13.389%	$279.7874	$279.79	$279.80	$279.80
Purchase #4	$63.48	11.850%	$71.0024	$71.00	$71.00	$71.00
Purchase #5	$33.67	12.122%	$37.7515	$37.75	$37.75	$37.80
Purchase #6	$143.68	11.130%	$159.6716	$159.67	$159.65	$159.70
Purchase #7	$48.76	10.767%	$54.01	$54.01	$54.00	$54.00
7 purchase totals =	$818.70		$900.8776	$900.87	$900.85	$901.00