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	$26.74	9.646%	$29.3193	$29.32	$29.30	$29.30
Purchase #2	$231.94	10.150%	$255.4819	$255.48	$255.50	$255.50
Purchase #3	$109.33	13.843%	$124.4646	$124.46	$124.45	$124.50
Purchase #4	$222.40	5.513%	$234.6609	$234.66	$234.65	$234.70
Purchase #5	$45.68	13.319%	$51.7641	$51.76	$51.75	$51.80
Purchase #6	$100.57	10.750%	$111.3813	$111.38	$111.40	$111.40
Purchase #7	$114.97	10.723%	$127.2982	$127.30	$127.30	$127.30
7 purchase totals =	$851.63		$934.3703	$934.36	$934.35	$934.50