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	$18.26	9.224%	$19.9443	$19.94	$19.95	$19.90
Purchase #2	$81.83	11.505%	$91.2445	$91.24	$91.25	$91.20
Purchase #3	$232.76	9.258%	$254.3089	$254.31	$254.30	$254.30
Purchase #4	$108.27	7.792%	$116.7064	$116.71	$116.70	$116.70
Purchase #5	$55.39	11.468%	$61.7421	$61.74	$61.75	$61.70
Purchase #6	$29.54	7.603%	$31.7859	$31.79	$31.80	$31.80
Purchase #7	$52.32	13.863%	$59.5731	$59.57	$59.55	$59.60
7 purchase totals =	$578.37		$635.3052	$635.30	$635.30	$635.20