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	$31.65	4.727%	$33.1461	$33.15	$33.15	$33.10
Purchase #2	$213.97	8.650%	$232.4784	$232.48	$232.50	$232.50
Purchase #3	$94.35	12.210%	$105.8701	$105.87	$105.85	$105.90
Purchase #4	$235.58	3.692%	$244.2776	$244.28	$244.30	$244.30
Purchase #5	$42.94	5.133%	$45.1441	$45.14	$45.15	$45.10
Purchase #6	$32.71	3.788%	$33.9491	$33.95	$33.95	$33.90
Purchase #7	$16.47	12.453%	$18.521	$18.52	$18.50	$18.50
7 purchase totals =	$667.67		$713.3864	$713.39	$713.40	$713.30