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	$96.45	12.446%	$108.4542	$108.45	$108.45	$108.50
Purchase #2	$198.36	9.334%	$216.8749	$216.87	$216.85	$216.90
Purchase #3	$104.65	12.346%	$117.5701	$117.57	$117.55	$117.60
Purchase #4	$110.71	7.427%	$118.9324	$118.93	$118.95	$118.90
Purchase #5	$189.67	5.814%	$200.6974	$200.70	$200.70	$200.70
Purchase #6	$138.43	10.351%	$152.7589	$152.76	$152.75	$152.80
Purchase #7	$37.54	13.317%	$42.5392	$42.54	$42.55	$42.50
7 purchase totals =	$875.81		$957.8271	$957.82	$957.80	$957.90