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	$48.72	3.706%	$50.5256	$50.53	$50.55	$50.50
Purchase #2	$74.82	5.232%	$78.7346	$78.73	$78.75	$78.70
Purchase #3	$212.55	6.266%	$225.8684	$225.87	$225.85	$225.90
Purchase #4	$235.50	9.682%	$258.3011	$258.30	$258.30	$258.30
Purchase #5	$87.52	8.445%	$94.9111	$94.91	$94.90	$94.90
Purchase #6	$59.29	3.741%	$61.508	$61.51	$61.50	$61.50
Purchase #7	$89.84	9.277%	$98.1745	$98.17	$98.15	$98.20
7 purchase totals =	$808.24		$868.0233	$868.02	$868.00	$868.00