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	$250.27	7.348%	$268.6598	$268.66	$268.65	$268.70
Purchase #2	$149.50	12.576%	$168.3011	$168.30	$168.30	$168.30
Purchase #3	$161.67	4.375%	$168.7431	$168.74	$168.75	$168.70
Purchase #4	$179.60	5.377%	$189.2571	$189.26	$189.25	$189.30
Purchase #5	$56.50	4.706%	$59.1589	$59.16	$59.15	$59.20
Purchase #6	$18.90	8.667%	$20.5381	$20.54	$20.55	$20.50
Purchase #7	$113.87	4.477%	$118.968	$118.97	$118.95	$119.00
7 purchase totals =	$930.31		$993.6261	$993.63	$993.60	$993.70