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	$139.95	11.870%	$156.5621	$156.56	$156.55	$156.60
Purchase #2	$74.84	4.310%	$78.0656	$78.07	$78.05	$78.10
Purchase #3	$112.44	6.239%	$119.4551	$119.46	$119.45	$119.50
Purchase #4	$154.90	13.386%	$175.6349	$175.63	$175.65	$175.60
Purchase #5	$123.91	10.344%	$136.7273	$136.73	$136.75	$136.70
Purchase #6	$121.83	7.759%	$131.2828	$131.28	$131.30	$131.30
Purchase #7	$34.49	13.732%	$39.2262	$39.23	$39.25	$39.20
7 purchase totals =	$762.36		$836.9540	$836.96	$837.00	$837.00