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	$46.48	10.864%	$51.5296	$51.53	$51.55	$51.50
Purchase #2	$96.85	3.673%	$100.4073	$100.41	$100.40	$100.40
Purchase #3	$46.93	9.168%	$51.2325	$51.23	$51.25	$51.20
Purchase #4	$13.93	7.486%	$14.9728	$14.97	$14.95	$15.00
Purchase #5	$85.47	11.808%	$95.5623	$95.56	$95.55	$95.60
Purchase #6	$107.56	13.808%	$122.4119	$122.41	$122.40	$122.40
Purchase #7	$94.59	10.847%	$104.8502	$104.85	$104.85	$104.90
7 purchase totals =	$491.81		$540.9666	$540.96	$540.95	$541.00