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	$134.56	3.680%	$139.5118	$139.51	$139.50	$139.50
Purchase #2	$198.33	9.528%	$217.2269	$217.23	$217.25	$217.20
Purchase #3	$14.50	4.260%	$15.1177	$15.12	$15.10	$15.10
Purchase #4	$85.29	10.657%	$94.3794	$94.38	$94.40	$94.40
Purchase #5	$36.41	11.850%	$40.7246	$40.72	$40.70	$40.70
Purchase #6	$225.31	12.422%	$253.298	$253.30	$253.30	$253.30
Purchase #7	$83.93	11.504%	$93.5853	$93.59	$93.60	$93.60
7 purchase totals =	$778.33		$853.8437	$853.85	$853.85	$853.80