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	$15.89	9.687%	$17.4293	$17.43	$17.45	$17.40
Purchase #2	$17.80	12.765%	$20.0722	$20.07	$20.05	$20.10
Purchase #3	$33.78	8.502%	$36.652	$36.65	$36.65	$36.70
Purchase #4	$158.34	10.392%	$174.7947	$174.79	$174.80	$174.80
Purchase #5	$246.48	4.102%	$256.5906	$256.59	$256.60	$256.60
Purchase #6	$36.36	5.653%	$38.4154	$38.42	$38.40	$38.40
Purchase #7	$182.64	7.611%	$196.5407	$196.54	$196.55	$196.50
7 purchase totals =	$691.29		$740.4949	$740.49	$740.50	$740.50