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	$238.80	8.692%	$259.5565	$259.56	$259.55	$259.60
Purchase #2	$89.34	12.311%	$100.3386	$100.34	$100.35	$100.30
Purchase #3	$68.41	3.733%	$70.9637	$70.96	$70.95	$71.00
Purchase #4	$238.29	13.497%	$270.452	$270.45	$270.45	$270.50
Purchase #5	$42.78	9.777%	$46.9626	$46.96	$46.95	$47.00
Purchase #6	$11.98	11.387%	$13.3442	$13.34	$13.35	$13.30
Purchase #7	$38.92	3.421%	$40.2515	$40.25	$40.25	$40.30
7 purchase totals =	$728.52		$801.8691	$801.86	$801.85	$802.00