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	$227.57	13.310%	$257.8596	$257.86	$257.85	$257.90
Purchase #2	$137.37	7.251%	$147.3307	$147.33	$147.35	$147.30
Purchase #3	$175.42	5.760%	$185.5242	$185.52	$185.50	$185.50
Purchase #4	$125.66	5.298%	$132.3175	$132.32	$132.30	$132.30
Purchase #5	$179.29	6.497%	$190.9385	$190.94	$190.95	$190.90
Purchase #6	$55.64	6.169%	$59.0724	$59.07	$59.05	$59.10
Purchase #7	$9.61	3.249%	$9.9222	$9.92	$9.90	$9.90
7 purchase totals =	$910.56		$982.9651	$982.96	$982.90	$982.90