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	$126.94	10.121%	$139.7876	$139.79	$139.80	$139.80
Purchase #2	$34.71	8.779%	$37.7572	$37.76	$37.75	$37.80
Purchase #3	$180.73	3.422%	$186.9146	$186.91	$186.90	$186.90
Purchase #4	$246.93	9.208%	$269.6673	$269.67	$269.65	$269.70
Purchase #5	$87.85	12.790%	$99.086	$99.09	$99.10	$99.10
Purchase #6	$132.91	6.765%	$141.9014	$141.90	$141.90	$141.90
Purchase #7	$160.85	13.518%	$182.5937	$182.59	$182.60	$182.60
7 purchase totals =	$970.92		$1,057.7078	$1,057.71	$1,057.70	$1,057.80