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	$170.72	11.554%	$190.445	$190.45	$190.45	$190.40
Purchase #2	$60.37	6.235%	$64.1341	$64.13	$64.15	$64.10
Purchase #3	$213.28	8.549%	$231.5133	$231.51	$231.50	$231.50
Purchase #4	$98.76	13.474%	$112.0669	$112.07	$112.05	$112.10
Purchase #5	$219.58	5.519%	$231.6986	$231.70	$231.70	$231.70
Purchase #6	$50.28	7.856%	$54.23	$54.23	$54.25	$54.20
Purchase #7	$31.79	6.261%	$33.7804	$33.78	$33.80	$33.80
7 purchase totals =	$844.78		$917.8683	$917.87	$917.90	$917.80