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	$49.52	11.807%	$55.3668	$55.37	$55.35	$55.40
Purchase #2	$226.56	9.204%	$247.4126	$247.41	$247.40	$247.40
Purchase #3	$6.94	9.504%	$7.5996	$7.60	$7.60	$7.60
Purchase #4	$18.50	8.233%	$20.0231	$20.02	$20.00	$20.00
Purchase #5	$220.81	13.403%	$250.4052	$250.41	$250.40	$250.40
Purchase #6	$246.33	11.453%	$274.5422	$274.54	$274.55	$274.50
Purchase #7	$234.93	6.325%	$249.7893	$249.79	$249.80	$249.80
7 purchase totals =	$1,003.59		$1,105.1388	$1,105.14	$1,105.10	$1,105.10