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	$103.47	4.868%	$108.5069	$108.51	$108.50	$108.50
Purchase #2	$84.47	3.434%	$87.3707	$87.37	$87.35	$87.40
Purchase #3	$11.25	9.649%	$12.3355	$12.34	$12.35	$12.30
Purchase #4	$95.46	9.412%	$104.4447	$104.44	$104.45	$104.40
Purchase #5	$135.75	3.608%	$140.6479	$140.65	$140.65	$140.60
Purchase #6	$28.57	3.281%	$29.5074	$29.51	$29.50	$29.50
Purchase #7	$72.88	8.189%	$78.8481	$78.85	$78.85	$78.80
7 purchase totals =	$531.85		$561.6612	$561.67	$561.65	$561.50