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	$29.77	11.820%	$33.2888	$33.29	$33.30	$33.30
Purchase #2	$90.66	11.168%	$100.7849	$100.78	$100.80	$100.80
Purchase #3	$169.46	12.181%	$190.1019	$190.10	$190.10	$190.10
Purchase #4	$241.94	12.854%	$273.039	$273.04	$273.05	$273.00
Purchase #5	$78.99	4.399%	$82.4648	$82.46	$82.45	$82.50
Purchase #6	$203.29	8.668%	$220.9112	$220.91	$220.90	$220.90
Purchase #7	$15.93	10.479%	$17.5993	$17.60	$17.60	$17.60
7 purchase totals =	$830.04		$918.1899	$918.18	$918.20	$918.20