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	$51.56	7.683%	$55.5214	$55.52	$55.50	$55.50
Purchase #2	$60.93	8.153%	$65.8976	$65.90	$65.90	$65.90
Purchase #3	$132.43	10.610%	$146.4808	$146.48	$146.50	$146.50
Purchase #4	$55.49	7.501%	$59.6523	$59.65	$59.65	$59.70
Purchase #5	$228.85	6.346%	$243.3728	$243.37	$243.35	$243.40
Purchase #6	$68.35	12.722%	$77.0455	$77.05	$77.05	$77.00
Purchase #7	$101.89	7.228%	$109.2546	$109.25	$109.25	$109.30
7 purchase totals =	$699.50		$757.2250	$757.22	$757.20	$757.30