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	$127.74	9.312%	$139.6351	$139.64	$139.65	$139.60
Purchase #2	$131.43	3.792%	$136.4138	$136.41	$136.40	$136.40
Purchase #3	$20.29	6.435%	$21.5957	$21.60	$21.60	$21.60
Purchase #4	$84.32	7.345%	$90.5133	$90.51	$90.50	$90.50
Purchase #5	$136.39	13.341%	$154.5858	$154.59	$154.60	$154.60
Purchase #6	$56.74	12.603%	$63.8909	$63.89	$63.90	$63.90
Purchase #7	$232.68	7.605%	$250.3753	$250.38	$250.40	$250.40
7 purchase totals =	$789.59		$857.0099	$857.02	$857.05	$857.00