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	$32.86	5.555%	$34.6854	$34.69	$34.70	$34.70
Purchase #2	$147.27	3.828%	$152.9075	$152.91	$152.90	$152.90
Purchase #3	$71.90	11.800%	$80.3842	$80.38	$80.40	$80.40
Purchase #4	$242.35	12.428%	$272.4693	$272.47	$272.45	$272.50
Purchase #5	$203.82	9.741%	$223.6741	$223.67	$223.65	$223.70
Purchase #6	$130.26	5.836%	$137.862	$137.86	$137.85	$137.90
Purchase #7	$80.58	12.803%	$90.8967	$90.90	$90.90	$90.90
7 purchase totals =	$909.04		$992.8792	$992.88	$992.85	$993.00