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	$76.40	6.634%	$81.4684	$81.47	$81.45	$81.50
Purchase #2	$50.62	5.390%	$53.3484	$53.35	$53.35	$53.30
Purchase #3	$197.32	8.187%	$213.4746	$213.47	$213.45	$213.50
Purchase #4	$74.67	11.766%	$83.4557	$83.46	$83.45	$83.50
Purchase #5	$208.53	7.106%	$223.3481	$223.35	$223.35	$223.30
Purchase #6	$104.96	8.346%	$113.72	$113.72	$113.70	$113.70
Purchase #7	$169.32	7.745%	$182.4338	$182.43	$182.45	$182.40
7 purchase totals =	$881.82		$951.2490	$951.25	$951.20	$951.20