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	$242.93	7.261%	$260.5691	$260.57	$260.55	$260.60
Purchase #2	$54.85	5.543%	$57.8903	$57.89	$57.90	$57.90
Purchase #3	$53.91	10.240%	$59.4304	$59.43	$59.45	$59.40
Purchase #4	$196.53	8.502%	$213.239	$213.24	$213.25	$213.20
Purchase #5	$122.53	12.541%	$137.8965	$137.90	$137.90	$137.90
Purchase #6	$40.74	13.573%	$46.2696	$46.27	$46.25	$46.30
Purchase #7	$14.54	4.698%	$15.2231	$15.22	$15.20	$15.20
7 purchase totals =	$726.03		$790.5180	$790.52	$790.50	$790.50