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	$10.44	13.579%	$11.8576	$11.86	$11.85	$11.90
Purchase #2	$17.43	13.849%	$19.8439	$19.84	$19.85	$19.80
Purchase #3	$202.86	9.473%	$222.0769	$222.08	$222.10	$222.10
Purchase #4	$155.47	12.592%	$175.0468	$175.05	$175.05	$175.00
Purchase #5	$85.78	5.583%	$90.5691	$90.57	$90.55	$90.60
Purchase #6	$234.48	8.797%	$255.1072	$255.11	$255.10	$255.10
Purchase #7	$126.95	9.749%	$139.3264	$139.33	$139.35	$139.30
7 purchase totals =	$833.41		$913.8279	$913.84	$913.85	$913.80