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	$123.59	10.135%	$136.1158	$136.12	$136.10	$136.10
Purchase #2	$69.77	10.259%	$76.9277	$76.93	$76.95	$76.90
Purchase #3	$74.27	4.724%	$77.7785	$77.78	$77.80	$77.80
Purchase #4	$80.35	12.712%	$90.5641	$90.56	$90.55	$90.60
Purchase #5	$193.54	4.339%	$201.9377	$201.94	$201.95	$201.90
Purchase #6	$62.80	13.622%	$71.3546	$71.35	$71.35	$71.40
Purchase #7	$150.71	9.796%	$165.4736	$165.47	$165.45	$165.50
7 purchase totals =	$755.03		$820.1520	$820.15	$820.15	$820.20