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	$14.85	4.548%	$15.5254	$15.53	$15.55	$15.50
Purchase #2	$248.72	10.136%	$273.9303	$273.93	$273.95	$273.90
Purchase #3	$40.42	4.357%	$42.1811	$42.18	$42.20	$42.20
Purchase #4	$46.54	3.151%	$48.0065	$48.01	$48.00	$48.00
Purchase #5	$216.59	6.610%	$230.9066	$230.91	$230.90	$230.90
Purchase #6	$213.25	8.117%	$230.5595	$230.56	$230.55	$230.60
Purchase #7	$221.49	8.511%	$240.341	$240.34	$240.35	$240.30
7 purchase totals =	$1,001.86		$1,081.4504	$1,081.46	$1,081.50	$1,081.40