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	$39.64	10.650%	$43.8617	$43.86	$43.85	$43.90
Purchase #2	$198.95	8.422%	$215.7056	$215.71	$215.70	$215.70
Purchase #3	$168.90	5.487%	$178.1675	$178.17	$178.15	$178.20
Purchase #4	$9.58	13.801%	$10.9021	$10.90	$10.90	$10.90
Purchase #5	$147.90	11.582%	$165.0298	$165.03	$165.05	$165.00
Purchase #6	$181.25	4.601%	$189.5893	$189.59	$189.60	$189.60
Purchase #7	$209.72	12.591%	$236.1258	$236.13	$236.15	$236.10
7 purchase totals =	$955.94		$1,039.3818	$1,039.39	$1,039.40	$1,039.40