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	$228.63	9.601%	$250.5808	$250.58	$250.60	$250.60
Purchase #2	$185.69	12.348%	$208.619	$208.62	$208.60	$208.60
Purchase #3	$209.50	7.725%	$225.6839	$225.68	$225.70	$225.70
Purchase #4	$40.25	12.840%	$45.4181	$45.42	$45.40	$45.40
Purchase #5	$116.56	12.782%	$131.4587	$131.46	$131.45	$131.50
Purchase #6	$216.82	12.736%	$244.4342	$244.43	$244.45	$244.40
Purchase #7	$37.77	6.689%	$40.2964	$40.30	$40.30	$40.30
7 purchase totals =	$1,035.22		$1,146.4911	$1,146.49	$1,146.50	$1,146.50