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	$121.46	12.715%	$136.9036	$136.90	$136.90	$136.90
Purchase #2	$35.58	10.870%	$39.4475	$39.45	$39.45	$39.40
Purchase #3	$147.96	5.801%	$156.5432	$156.54	$156.55	$156.50
Purchase #4	$41.55	11.460%	$46.3116	$46.31	$46.30	$46.30
Purchase #5	$178.96	6.608%	$190.7857	$190.79	$190.80	$190.80
Purchase #6	$21.61	13.854%	$24.6038	$24.60	$24.60	$24.60
Purchase #7	$219.59	9.285%	$239.9789	$239.98	$240.00	$240.00
7 purchase totals =	$766.71		$834.5743	$834.57	$834.60	$834.50