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	$17.65	7.350%	$18.9473	$18.95	$18.95	$18.90
Purchase #2	$151.59	13.820%	$172.5397	$172.54	$172.55	$172.50
Purchase #3	$131.88	3.797%	$136.8875	$136.89	$136.90	$136.90
Purchase #4	$81.61	9.695%	$89.5221	$89.52	$89.50	$89.50
Purchase #5	$116.61	6.288%	$123.9424	$123.94	$123.95	$123.90
Purchase #6	$169.70	5.373%	$178.818	$178.82	$178.80	$178.80
Purchase #7	$43.38	13.733%	$49.3374	$49.34	$49.35	$49.30
7 purchase totals =	$712.42		$769.9944	$770.00	$770.00	$769.80