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	$198.72	10.163%	$218.9159	$218.92	$218.90	$218.90
Purchase #2	$69.71	9.870%	$76.5904	$76.59	$76.60	$76.60
Purchase #3	$224.65	11.354%	$250.1568	$250.16	$250.15	$250.20
Purchase #4	$248.41	13.387%	$281.6646	$281.66	$281.65	$281.70
Purchase #5	$66.85	4.431%	$69.8121	$69.81	$69.80	$69.80
Purchase #6	$29.43	8.358%	$31.8898	$31.89	$31.90	$31.90
Purchase #7	$37.29	9.546%	$40.8497	$40.85	$40.85	$40.80
7 purchase totals =	$875.06		$969.8793	$969.88	$969.85	$969.90