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	$22.77	9.130%	$24.8489	$24.85	$24.85	$24.80
Purchase #2	$45.34	3.743%	$47.0371	$47.04	$47.05	$47.00
Purchase #3	$94.43	6.749%	$100.8031	$100.80	$100.80	$100.80
Purchase #4	$171.93	4.628%	$179.8869	$179.89	$179.90	$179.90
Purchase #5	$212.43	10.409%	$234.5418	$234.54	$234.55	$234.50
Purchase #6	$250.57	12.472%	$281.8211	$281.82	$281.80	$281.80
Purchase #7	$38.50	13.758%	$43.7968	$43.80	$43.80	$43.80
7 purchase totals =	$835.97		$912.7357	$912.74	$912.75	$912.60