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	$185.46	12.211%	$208.1065	$208.11	$208.10	$208.10
Purchase #2	$156.63	6.746%	$167.1963	$167.20	$167.20	$167.20
Purchase #3	$231.79	10.244%	$255.5346	$255.53	$255.55	$255.50
Purchase #4	$208.40	6.558%	$222.0669	$222.07	$222.05	$222.10
Purchase #5	$111.74	6.776%	$119.3115	$119.31	$119.30	$119.30
Purchase #6	$109.49	9.785%	$120.2036	$120.20	$120.20	$120.20
Purchase #7	$40.32	6.500%	$42.9408	$42.94	$42.95	$42.90
7 purchase totals =	$1,043.83		$1,135.3602	$1,135.36	$1,135.35	$1,135.30