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	$6.93	6.471%	$7.3784	$7.38	$7.40	$7.40
Purchase #2	$135.35	11.262%	$150.5931	$150.59	$150.60	$150.60
Purchase #3	$174.25	6.728%	$185.9735	$185.97	$185.95	$186.00
Purchase #4	$132.77	11.290%	$147.7597	$147.76	$147.75	$147.80
Purchase #5	$133.69	13.527%	$151.7742	$151.77	$151.75	$151.80
Purchase #6	$221.59	12.725%	$249.7873	$249.79	$249.80	$249.80
Purchase #7	$190.98	8.177%	$206.5964	$206.60	$206.60	$206.60
7 purchase totals =	$995.56		$1,099.8626	$1,099.86	$1,099.85	$1,100.00