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	$135.91	3.306%	$140.4032	$140.40	$140.40	$140.40
Purchase #2	$111.51	11.114%	$123.9032	$123.90	$123.90	$123.90
Purchase #3	$88.91	7.638%	$95.7009	$95.70	$95.70	$95.70
Purchase #4	$20.81	4.858%	$21.8209	$21.82	$21.80	$21.80
Purchase #5	$76.88	8.452%	$83.3779	$83.38	$83.40	$83.40
Purchase #6	$130.77	9.481%	$143.1683	$143.17	$143.15	$143.20
Purchase #7	$211.69	7.475%	$227.5138	$227.51	$227.50	$227.50
7 purchase totals =	$776.48		$835.8882	$835.88	$835.85	$835.90