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	$41.90	3.528%	$43.3782	$43.38	$43.40	$43.40
Purchase #2	$50.85	9.746%	$55.8058	$55.81	$55.80	$55.80
Purchase #3	$36.93	11.660%	$41.236	$41.24	$41.25	$41.20
Purchase #4	$178.38	6.572%	$190.1031	$190.10	$190.10	$190.10
Purchase #5	$56.57	4.680%	$59.2175	$59.22	$59.20	$59.20
Purchase #6	$10.72	7.442%	$11.5178	$11.52	$11.50	$11.50
Purchase #7	$237.52	11.620%	$265.1198	$265.12	$265.10	$265.10
7 purchase totals =	$612.87		$666.3782	$666.39	$666.35	$666.30