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	$40.31	9.502%	$44.1403	$44.14	$44.15	$44.10
Purchase #2	$42.79	13.418%	$48.5316	$48.53	$48.55	$48.50
Purchase #3	$162.84	13.394%	$184.6508	$184.65	$184.65	$184.70
Purchase #4	$234.50	5.276%	$246.8722	$246.87	$246.85	$246.90
Purchase #5	$172.59	7.727%	$185.926	$185.93	$185.95	$185.90
Purchase #6	$71.60	10.164%	$78.8774	$78.88	$78.90	$78.90
Purchase #7	$85.57	6.232%	$90.9027	$90.90	$90.90	$90.90
7 purchase totals =	$810.20		$879.9010	$879.90	$879.95	$879.90