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	$89.60	12.138%	$100.4756	$100.48	$100.50	$100.50
Purchase #2	$83.55	7.145%	$89.5196	$89.52	$89.50	$89.50
Purchase #3	$179.59	10.265%	$198.0249	$198.02	$198.00	$198.00
Purchase #4	$197.66	9.432%	$216.3033	$216.30	$216.30	$216.30
Purchase #5	$175.55	5.454%	$185.1245	$185.12	$185.10	$185.10
Purchase #6	$136.39	9.611%	$149.4984	$149.50	$149.50	$149.50
Purchase #7	$6.50	8.545%	$7.0554	$7.06	$7.05	$7.10
7 purchase totals =	$868.84		$946.0017	$946.00	$945.95	$946.00