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	$250.28	13.709%	$284.5909	$284.59	$284.60	$284.60
Purchase #2	$126.65	4.444%	$132.2783	$132.28	$132.30	$132.30
Purchase #3	$38.53	3.261%	$39.7865	$39.79	$39.80	$39.80
Purchase #4	$126.54	13.505%	$143.6292	$143.63	$143.65	$143.60
Purchase #5	$73.66	11.168%	$81.8863	$81.89	$81.90	$81.90
Purchase #6	$18.46	11.568%	$20.5955	$20.60	$20.60	$20.60
Purchase #7	$18.52	6.197%	$19.6677	$19.67	$19.65	$19.70
7 purchase totals =	$652.64		$722.4344	$722.45	$722.50	$722.50