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	$42.42	6.778%	$45.2952	$45.30	$45.30	$45.30
Purchase #2	$203.85	11.424%	$227.1378	$227.14	$227.15	$227.10
Purchase #3	$17.46	6.344%	$18.5677	$18.57	$18.55	$18.60
Purchase #4	$137.45	4.117%	$143.1088	$143.11	$143.10	$143.10
Purchase #5	$121.98	9.727%	$133.845	$133.85	$133.85	$133.80
Purchase #6	$151.61	9.655%	$166.2479	$166.25	$166.25	$166.20
Purchase #7	$94.44	11.487%	$105.2883	$105.29	$105.30	$105.30
7 purchase totals =	$769.21		$839.4907	$839.51	$839.50	$839.40