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	$53.75	10.667%	$59.4835	$59.48	$59.50	$59.50
Purchase #2	$32.47	9.621%	$35.5939	$35.59	$35.60	$35.60
Purchase #3	$212.94	6.846%	$227.5179	$227.52	$227.50	$227.50
Purchase #4	$205.56	8.724%	$223.4931	$223.49	$223.50	$223.50
Purchase #5	$38.33	10.473%	$42.3443	$42.34	$42.35	$42.30
Purchase #6	$219.85	8.412%	$238.3438	$238.34	$238.35	$238.30
Purchase #7	$14.96	11.734%	$16.7154	$16.72	$16.70	$16.70
7 purchase totals =	$777.86		$843.4919	$843.48	$843.50	$843.40