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	$28.61	11.526%	$31.9076	$31.91	$31.90	$31.90
Purchase #2	$94.52	6.351%	$100.523	$100.52	$100.50	$100.50
Purchase #3	$133.33	5.586%	$140.7778	$140.78	$140.80	$140.80
Purchase #4	$203.93	8.388%	$221.0356	$221.04	$221.05	$221.00
Purchase #5	$125.99	10.656%	$139.4155	$139.42	$139.40	$139.40
Purchase #6	$203.81	7.187%	$218.4578	$218.46	$218.45	$218.50
Purchase #7	$132.75	13.381%	$150.5133	$150.51	$150.50	$150.50
7 purchase totals =	$922.94		$1,002.6306	$1,002.64	$1,002.60	$1,002.60