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	$47.89	6.148%	$50.8343	$50.83	$50.85	$50.80
Purchase #2	$61.79	12.723%	$69.6515	$69.65	$69.65	$69.70
Purchase #3	$9.57	9.659%	$10.4944	$10.49	$10.50	$10.50
Purchase #4	$139.48	3.148%	$143.8708	$143.87	$143.85	$143.90
Purchase #5	$95.60	10.804%	$105.9286	$105.93	$105.95	$105.90
Purchase #6	$201.54	3.476%	$208.5455	$208.55	$208.55	$208.50
Purchase #7	$56.40	5.288%	$59.3824	$59.38	$59.40	$59.40
7 purchase totals =	$612.27		$648.7075	$648.70	$648.75	$648.70