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	$36.50	3.860%	$37.9089	$37.91	$37.90	$37.90
Purchase #2	$239.99	13.701%	$272.871	$272.87	$272.85	$272.90
Purchase #3	$36.57	3.758%	$37.9443	$37.94	$37.95	$37.90
Purchase #4	$113.56	10.828%	$125.8563	$125.86	$125.85	$125.90
Purchase #5	$52.52	3.692%	$54.459	$54.46	$54.45	$54.50
Purchase #6	$177.71	12.340%	$199.6394	$199.64	$199.65	$199.60
Purchase #7	$227.40	12.749%	$256.3912	$256.39	$256.40	$256.40
7 purchase totals =	$884.25		$985.0701	$985.07	$985.05	$985.10