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	$156.72	9.636%	$171.8215	$171.82	$171.80	$171.80
Purchase #2	$177.41	8.544%	$192.5679	$192.57	$192.55	$192.60
Purchase #3	$119.71	6.295%	$127.2457	$127.25	$127.25	$127.20
Purchase #4	$209.78	12.716%	$236.4556	$236.46	$236.45	$236.50
Purchase #5	$235.61	4.388%	$245.9486	$245.95	$245.95	$245.90
Purchase #6	$217.58	7.767%	$234.4794	$234.48	$234.50	$234.50
Purchase #7	$83.43	8.546%	$90.5599	$90.56	$90.55	$90.60
7 purchase totals =	$1,200.24		$1,299.0786	$1,299.09	$1,299.05	$1,299.10