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	$198.54	12.180%	$222.7222	$222.72	$222.70	$222.70
Purchase #2	$160.26	3.859%	$166.4444	$166.44	$166.45	$166.40
Purchase #3	$39.46	13.598%	$44.8258	$44.83	$44.85	$44.80
Purchase #4	$110.82	6.484%	$118.0056	$118.01	$118.00	$118.00
Purchase #5	$210.40	6.535%	$224.1496	$224.15	$224.15	$224.10
Purchase #6	$40.89	13.581%	$46.4433	$46.44	$46.45	$46.40
Purchase #7	$158.25	11.168%	$175.9234	$175.92	$175.90	$175.90
7 purchase totals =	$918.62		$998.5143	$998.51	$998.50	$998.30