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	$80.64	9.638%	$88.4121	$88.41	$88.40	$88.40
Purchase #2	$87.96	3.127%	$90.7105	$90.71	$90.70	$90.70
Purchase #3	$137.49	8.706%	$149.4599	$149.46	$149.45	$149.50
Purchase #4	$88.57	12.290%	$99.4553	$99.46	$99.45	$99.50
Purchase #5	$197.64	12.219%	$221.7896	$221.79	$221.80	$221.80
Purchase #6	$138.71	4.452%	$144.8854	$144.89	$144.90	$144.90
Purchase #7	$136.54	6.123%	$144.9003	$144.90	$144.90	$144.90
7 purchase totals =	$867.55		$939.6131	$939.62	$939.60	$939.70