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	$58.81	13.439%	$66.7135	$66.71	$66.70	$66.70
Purchase #2	$19.30	10.363%	$21.3001	$21.30	$21.30	$21.30
Purchase #3	$88.30	12.731%	$99.5415	$99.54	$99.55	$99.50
Purchase #4	$139.56	7.776%	$150.4122	$150.41	$150.40	$150.40
Purchase #5	$123.35	11.244%	$137.2195	$137.22	$137.20	$137.20
Purchase #6	$112.95	11.417%	$125.8455	$125.85	$125.85	$125.80
Purchase #7	$105.44	13.519%	$119.6944	$119.69	$119.70	$119.70
7 purchase totals =	$647.71		$720.7267	$720.72	$720.70	$720.60