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	$100.52	7.801%	$108.3616	$108.36	$108.35	$108.40
Purchase #2	$116.47	12.411%	$130.9251	$130.93	$130.95	$130.90
Purchase #3	$102.29	5.859%	$108.2832	$108.28	$108.30	$108.30
Purchase #4	$208.33	9.211%	$227.5193	$227.52	$227.50	$227.50
Purchase #5	$226.66	9.130%	$247.3541	$247.35	$247.35	$247.40
Purchase #6	$28.96	7.422%	$31.1094	$31.11	$31.10	$31.10
Purchase #7	$195.67	6.262%	$207.9229	$207.92	$207.90	$207.90
7 purchase totals =	$978.90		$1,061.4756	$1,061.47	$1,061.45	$1,061.50