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	$247.85	3.170%	$255.7068	$255.71	$255.70	$255.70
Purchase #2	$200.85	13.443%	$227.8503	$227.85	$227.85	$227.90
Purchase #3	$244.32	12.244%	$274.2345	$274.23	$274.25	$274.20
Purchase #4	$132.50	8.242%	$143.4207	$143.42	$143.40	$143.40
Purchase #5	$213.56	3.593%	$221.2332	$221.23	$221.25	$221.20
Purchase #6	$5.41	6.546%	$5.7641	$5.76	$5.75	$5.80
Purchase #7	$152.34	12.614%	$171.5562	$171.56	$171.55	$171.60
7 purchase totals =	$1,196.83		$1,299.7658	$1,299.76	$1,299.75	$1,299.80