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	$232.42	6.844%	$248.3268	$248.33	$248.35	$248.30
Purchase #2	$82.86	9.611%	$90.8237	$90.82	$90.80	$90.80
Purchase #3	$225.95	7.240%	$242.3088	$242.31	$242.30	$242.30
Purchase #4	$5.93	11.192%	$6.5937	$6.59	$6.60	$6.60
Purchase #5	$55.90	7.490%	$60.0869	$60.09	$60.10	$60.10
Purchase #6	$39.65	8.175%	$42.8914	$42.89	$42.90	$42.90
Purchase #7	$244.61	6.630%	$260.8276	$260.83	$260.85	$260.80
7 purchase totals =	$887.32		$951.8589	$951.86	$951.90	$951.80