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	$23.52	7.576%	$25.3019	$25.30	$25.30	$25.30
Purchase #2	$219.75	9.590%	$240.824	$240.82	$240.80	$240.80
Purchase #3	$138.93	9.124%	$151.606	$151.61	$151.60	$151.60
Purchase #4	$82.88	12.598%	$93.3212	$93.32	$93.30	$93.30
Purchase #5	$244.56	13.801%	$278.3117	$278.31	$278.30	$278.30
Purchase #6	$45.94	5.427%	$48.4332	$48.43	$48.45	$48.40
Purchase #7	$114.88	7.166%	$123.1123	$123.11	$123.10	$123.10
7 purchase totals =	$870.46		$960.9103	$960.90	$960.85	$960.80