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	$19.46	7.394%	$20.8989	$20.90	$20.90	$20.90
Purchase #2	$126.80	3.593%	$131.3559	$131.36	$131.35	$131.40
Purchase #3	$78.30	6.537%	$83.4185	$83.42	$83.40	$83.40
Purchase #4	$21.41	9.258%	$23.3921	$23.39	$23.40	$23.40
Purchase #5	$120.72	8.574%	$131.0705	$131.07	$131.05	$131.10
Purchase #6	$62.79	9.799%	$68.9428	$68.94	$68.95	$68.90
Purchase #7	$143.75	8.388%	$155.8078	$155.81	$155.80	$155.80
7 purchase totals =	$573.23		$614.8865	$614.89	$614.85	$614.90