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	$140.60	4.295%	$146.6388	$146.64	$146.65	$146.60
Purchase #2	$171.43	7.532%	$184.3421	$184.34	$184.35	$184.30
Purchase #3	$117.64	12.641%	$132.5109	$132.51	$132.50	$132.50
Purchase #4	$62.29	13.146%	$70.4786	$70.48	$70.50	$70.50
Purchase #5	$95.31	9.463%	$104.3292	$104.33	$104.35	$104.30
Purchase #6	$122.69	13.328%	$139.0421	$139.04	$139.05	$139.00
Purchase #7	$130.90	11.115%	$145.4495	$145.45	$145.45	$145.40
7 purchase totals =	$840.86		$922.7912	$922.79	$922.85	$922.60