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	$144.72	12.297%	$162.5162	$162.52	$162.50	$162.50
Purchase #2	$112.61	6.527%	$119.9601	$119.96	$119.95	$120.00
Purchase #3	$16.28	13.535%	$18.4835	$18.48	$18.50	$18.50
Purchase #4	$133.71	5.404%	$140.9357	$140.94	$140.95	$140.90
Purchase #5	$126.25	8.749%	$137.2956	$137.30	$137.30	$137.30
Purchase #6	$131.48	4.125%	$136.9036	$136.90	$136.90	$136.90
Purchase #7	$203.64	10.586%	$225.1973	$225.20	$225.20	$225.20
7 purchase totals =	$868.69		$941.2920	$941.30	$941.30	$941.30