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	$160.46	6.680%	$171.1787	$171.18	$171.20	$171.20
Purchase #2	$236.52	4.173%	$246.39	$246.39	$246.40	$246.40
Purchase #3	$78.69	11.506%	$87.7441	$87.74	$87.75	$87.70
Purchase #4	$95.86	8.261%	$103.779	$103.78	$103.80	$103.80
Purchase #5	$91.83	13.759%	$104.4649	$104.46	$104.45	$104.50
Purchase #6	$115.39	13.679%	$131.1742	$131.17	$131.15	$131.20
Purchase #7	$125.69	11.693%	$140.3869	$140.39	$140.40	$140.40
7 purchase totals =	$904.44		$985.1178	$985.11	$985.15	$985.20