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	$75.38	3.859%	$78.2889	$78.29	$78.30	$78.30
Purchase #2	$151.93	13.479%	$172.4086	$172.41	$172.40	$172.40
Purchase #3	$65.59	9.456%	$71.7922	$71.79	$71.80	$71.80
Purchase #4	$220.31	11.189%	$244.9605	$244.96	$244.95	$245.00
Purchase #5	$244.75	10.698%	$270.9334	$270.93	$270.95	$270.90
Purchase #6	$65.58	8.443%	$71.1169	$71.12	$71.10	$71.10
Purchase #7	$177.44	13.540%	$201.4654	$201.47	$201.45	$201.50
7 purchase totals =	$1,000.98		$1,110.9659	$1,110.97	$1,110.95	$1,111.00