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	$80.25	12.339%	$90.152	$90.15	$90.15	$90.20
Purchase #2	$14.60	8.812%	$15.8866	$15.89	$15.90	$15.90
Purchase #3	$107.25	8.270%	$116.1196	$116.12	$116.10	$116.10
Purchase #4	$245.91	4.339%	$256.58	$256.58	$256.60	$256.60
Purchase #5	$172.48	7.785%	$185.9076	$185.91	$185.90	$185.90
Purchase #6	$224.59	13.799%	$255.5812	$255.58	$255.60	$255.60
Purchase #7	$69.30	5.810%	$73.3263	$73.33	$73.35	$73.30
7 purchase totals =	$914.38		$993.5533	$993.56	$993.60	$993.60