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	$67.63	4.844%	$70.906	$70.91	$70.90	$70.90
Purchase #2	$96.59	3.814%	$100.2739	$100.27	$100.25	$100.30
Purchase #3	$28.78	11.252%	$32.0183	$32.02	$32.00	$32.00
Purchase #4	$76.71	7.410%	$82.3942	$82.39	$82.40	$82.40
Purchase #5	$142.56	8.594%	$154.8116	$154.81	$154.80	$154.80
Purchase #6	$209.53	13.175%	$237.1356	$237.14	$237.15	$237.10
Purchase #7	$245.58	13.493%	$278.7161	$278.72	$278.70	$278.70
7 purchase totals =	$867.38		$956.2557	$956.26	$956.20	$956.20