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	$31.55	5.398%	$33.2531	$33.25	$33.25	$33.30
Purchase #2	$105.72	3.691%	$109.6221	$109.62	$109.60	$109.60
Purchase #3	$173.81	10.566%	$192.1748	$192.17	$192.15	$192.20
Purchase #4	$117.58	3.297%	$121.4566	$121.46	$121.45	$121.50
Purchase #5	$249.65	9.783%	$274.0733	$274.07	$274.05	$274.10
Purchase #6	$209.68	10.390%	$231.4658	$231.47	$231.45	$231.50
Purchase #7	$49.31	12.784%	$55.6138	$55.61	$55.60	$55.60
7 purchase totals =	$937.30		$1,017.6595	$1,017.65	$1,017.55	$1,017.80