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	$71.59	12.355%	$80.4349	$80.43	$80.45	$80.40
Purchase #2	$126.83	10.452%	$140.0863	$140.09	$140.10	$140.10
Purchase #3	$149.45	3.312%	$154.3998	$154.40	$154.40	$154.40
Purchase #4	$10.41	5.121%	$10.9431	$10.94	$10.95	$10.90
Purchase #5	$152.65	8.651%	$165.8558	$165.86	$165.85	$165.90
Purchase #6	$246.94	4.681%	$258.4993	$258.50	$258.50	$258.50
Purchase #7	$140.38	4.406%	$146.5651	$146.57	$146.55	$146.60
7 purchase totals =	$898.25		$956.7843	$956.79	$956.80	$956.80