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	$18.94	7.866%	$20.4298	$20.43	$20.45	$20.40
Purchase #2	$136.35	11.406%	$151.9021	$151.90	$151.90	$151.90
Purchase #3	$145.29	7.475%	$156.1504	$156.15	$156.15	$156.20
Purchase #4	$180.26	9.138%	$196.7322	$196.73	$196.75	$196.70
Purchase #5	$56.46	9.842%	$62.0168	$62.02	$62.00	$62.00
Purchase #6	$192.37	10.471%	$212.5131	$212.51	$212.50	$212.50
Purchase #7	$124.61	6.303%	$132.4642	$132.46	$132.45	$132.50
7 purchase totals =	$854.28		$932.2086	$932.20	$932.20	$932.20