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	$67.65	6.183%	$71.8328	$71.83	$71.85	$71.80
Purchase #2	$36.39	10.487%	$40.2062	$40.21	$40.20	$40.20
Purchase #3	$107.80	10.678%	$119.3109	$119.31	$119.30	$119.30
Purchase #4	$42.41	6.291%	$45.078	$45.08	$45.10	$45.10
Purchase #5	$29.84	8.353%	$32.3325	$32.33	$32.35	$32.30
Purchase #6	$135.88	9.767%	$149.1514	$149.15	$149.15	$149.20
Purchase #7	$41.90	8.642%	$45.521	$45.52	$45.50	$45.50
7 purchase totals =	$461.87		$503.4328	$503.43	$503.45	$503.40