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	$112.50	5.224%	$118.377	$118.38	$118.40	$118.40
Purchase #2	$70.39	6.324%	$74.8415	$74.84	$74.85	$74.80
Purchase #3	$135.89	5.179%	$142.9277	$142.93	$142.95	$142.90
Purchase #4	$95.81	11.539%	$106.8655	$106.87	$106.85	$106.90
Purchase #5	$84.51	7.178%	$90.5761	$90.58	$90.60	$90.60
Purchase #6	$236.77	10.860%	$262.4832	$262.48	$262.50	$262.50
Purchase #7	$136.95	4.847%	$143.588	$143.59	$143.60	$143.60
7 purchase totals =	$872.82		$939.6590	$939.67	$939.75	$939.70