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	$131.37	6.193%	$139.5057	$139.51	$139.50	$139.50
Purchase #2	$80.87	8.552%	$87.786	$87.79	$87.80	$87.80
Purchase #3	$39.87	9.768%	$43.7645	$43.76	$43.75	$43.80
Purchase #4	$249.62	8.800%	$271.5866	$271.59	$271.60	$271.60
Purchase #5	$179.89	13.243%	$203.7128	$203.71	$203.70	$203.70
Purchase #6	$233.78	12.457%	$262.902	$262.90	$262.90	$262.90
Purchase #7	$29.31	8.741%	$31.872	$31.87	$31.85	$31.90
7 purchase totals =	$944.71		$1,041.1296	$1,041.13	$1,041.10	$1,041.20