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	$231.32	6.545%	$246.4599	$246.46	$246.45	$246.50
Purchase #2	$179.65	11.347%	$200.0349	$200.03	$200.05	$200.00
Purchase #3	$95.91	4.494%	$100.2202	$100.22	$100.20	$100.20
Purchase #4	$39.32	3.213%	$40.5834	$40.58	$40.60	$40.60
Purchase #5	$190.50	5.271%	$200.5413	$200.54	$200.55	$200.50
Purchase #6	$22.83	7.217%	$24.4776	$24.48	$24.50	$24.50
Purchase #7	$169.89	5.831%	$179.7963	$179.80	$179.80	$179.80
7 purchase totals =	$929.42		$992.1136	$992.11	$992.15	$992.10