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	$110.39	13.138%	$124.893	$124.89	$124.90	$124.90
Purchase #2	$206.72	3.466%	$213.8849	$213.88	$213.90	$213.90
Purchase #3	$223.64	11.514%	$249.3899	$249.39	$249.40	$249.40
Purchase #4	$127.36	7.531%	$136.9515	$136.95	$136.95	$137.00
Purchase #5	$190.94	5.709%	$201.8408	$201.84	$201.85	$201.80
Purchase #6	$241.86	5.575%	$255.3437	$255.34	$255.35	$255.30
Purchase #7	$67.75	7.449%	$72.7967	$72.80	$72.80	$72.80
7 purchase totals =	$1,168.66		$1,255.1005	$1,255.09	$1,255.15	$1,255.10