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	$25.57	8.870%	$27.8381	$27.84	$27.85	$27.80
Purchase #2	$12.84	6.442%	$13.6672	$13.67	$13.65	$13.70
Purchase #3	$178.25	6.707%	$190.2052	$190.21	$190.20	$190.20
Purchase #4	$205.32	13.733%	$233.5166	$233.52	$233.50	$233.50
Purchase #5	$215.78	13.329%	$244.5413	$244.54	$244.55	$244.50
Purchase #6	$82.71	3.787%	$85.8422	$85.84	$85.85	$85.80
Purchase #7	$136.81	3.683%	$141.8487	$141.85	$141.85	$141.80
7 purchase totals =	$857.28		$937.4593	$937.47	$937.45	$937.30