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	$83.37	6.632%	$88.8991	$88.90	$88.90	$88.90
Purchase #2	$201.47	8.434%	$218.462	$218.46	$218.45	$218.50
Purchase #3	$145.56	10.805%	$161.2878	$161.29	$161.30	$161.30
Purchase #4	$231.84	13.390%	$262.8834	$262.88	$262.90	$262.90
Purchase #5	$39.61	12.517%	$44.568	$44.57	$44.55	$44.60
Purchase #6	$6.83	4.736%	$7.1535	$7.15	$7.15	$7.20
Purchase #7	$102.32	10.332%	$112.8917	$112.89	$112.90	$112.90
7 purchase totals =	$811.00		$896.1455	$896.14	$896.15	$896.30