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	$245.59	13.562%	$278.8969	$278.90	$278.90	$278.90
Purchase #2	$59.26	12.836%	$66.8666	$66.87	$66.85	$66.90
Purchase #3	$204.83	12.311%	$230.0466	$230.05	$230.05	$230.00
Purchase #4	$170.64	11.231%	$189.8046	$189.80	$189.80	$189.80
Purchase #5	$90.38	11.483%	$100.7583	$100.76	$100.75	$100.80
Purchase #6	$45.74	6.250%	$48.5988	$48.60	$48.60	$48.60
Purchase #7	$137.68	8.157%	$148.9106	$148.91	$148.90	$148.90
7 purchase totals =	$954.12		$1,063.8824	$1,063.89	$1,063.85	$1,063.90