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	$11.25	11.256%	$12.5163	$12.52	$12.50	$12.50
Purchase #2	$107.81	4.131%	$112.2636	$112.26	$112.25	$112.30
Purchase #3	$67.93	11.796%	$75.943	$75.94	$75.95	$75.90
Purchase #4	$142.67	6.467%	$151.8965	$151.90	$151.90	$151.90
Purchase #5	$210.32	8.163%	$227.4884	$227.49	$227.50	$227.50
Purchase #6	$203.53	11.666%	$227.2738	$227.27	$227.25	$227.30
Purchase #7	$35.43	13.860%	$40.3406	$40.34	$40.35	$40.30
7 purchase totals =	$778.94		$847.7222	$847.72	$847.70	$847.70