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	$20.48	13.354%	$23.2149	$23.21	$23.20	$23.20
Purchase #2	$150.41	4.252%	$156.8054	$156.81	$156.80	$156.80
Purchase #3	$74.73	10.537%	$82.6043	$82.60	$82.60	$82.60
Purchase #4	$65.86	8.767%	$71.6339	$71.63	$71.65	$71.60
Purchase #5	$232.89	11.263%	$259.1204	$259.12	$259.10	$259.10
Purchase #6	$137.56	6.559%	$146.5826	$146.58	$146.60	$146.60
Purchase #7	$14.66	8.744%	$15.9419	$15.94	$15.95	$15.90
7 purchase totals =	$696.59		$755.9034	$755.89	$755.90	$755.80