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	$54.93	4.119%	$57.1926	$57.19	$57.20	$57.20
Purchase #2	$159.41	4.395%	$166.4161	$166.42	$166.40	$166.40
Purchase #3	$172.92	4.604%	$180.8812	$180.88	$180.90	$180.90
Purchase #4	$142.85	13.325%	$161.8848	$161.88	$161.90	$161.90
Purchase #5	$6.51	13.249%	$7.3725	$7.37	$7.35	$7.40
Purchase #6	$144.78	10.120%	$159.4317	$159.43	$159.45	$159.40
Purchase #7	$126.49	13.317%	$143.3347	$143.33	$143.35	$143.30
7 purchase totals =	$807.89		$876.5136	$876.50	$876.55	$876.50