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	$29.87	10.110%	$32.8899	$32.89	$32.90	$32.90
Purchase #2	$126.89	13.640%	$144.1978	$144.20	$144.20	$144.20
Purchase #3	$125.33	8.808%	$136.3691	$136.37	$136.35	$136.40
Purchase #4	$230.28	11.735%	$257.3034	$257.30	$257.30	$257.30
Purchase #5	$205.50	8.650%	$223.2758	$223.28	$223.30	$223.30
Purchase #6	$21.40	5.662%	$22.6117	$22.61	$22.60	$22.60
Purchase #7	$141.30	10.833%	$156.607	$156.61	$156.60	$156.60
7 purchase totals =	$880.57		$973.2547	$973.26	$973.25	$973.30