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	$214.46	11.160%	$238.3937	$238.39	$238.40	$238.40
Purchase #2	$34.97	6.348%	$37.1899	$37.19	$37.20	$37.20
Purchase #3	$104.39	4.694%	$109.2901	$109.29	$109.30	$109.30
Purchase #4	$179.86	11.644%	$200.8029	$200.80	$200.80	$200.80
Purchase #5	$29.49	7.287%	$31.6389	$31.64	$31.65	$31.60
Purchase #6	$124.69	9.197%	$136.1577	$136.16	$136.15	$136.20
Purchase #7	$97.65	4.590%	$102.1321	$102.13	$102.15	$102.10
7 purchase totals =	$785.51		$855.6053	$855.60	$855.65	$855.60