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	$63.91	11.672%	$71.3696	$71.37	$71.35	$71.40
Purchase #2	$78.51	5.104%	$82.5172	$82.52	$82.50	$82.50
Purchase #3	$204.95	12.172%	$229.8965	$229.90	$229.90	$229.90
Purchase #4	$242.92	12.631%	$273.6032	$273.60	$273.60	$273.60
Purchase #5	$129.86	8.332%	$140.6799	$140.68	$140.70	$140.70
Purchase #6	$229.33	11.551%	$255.8199	$255.82	$255.80	$255.80
Purchase #7	$219.64	3.665%	$227.6898	$227.69	$227.70	$227.70
7 purchase totals =	$1,169.12		$1,281.5761	$1,281.58	$1,281.55	$1,281.60