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	$47.72	8.683%	$51.8635	$51.86	$51.85	$51.90
Purchase #2	$111.26	11.358%	$123.8969	$123.90	$123.90	$123.90
Purchase #3	$86.32	10.433%	$95.3258	$95.33	$95.35	$95.30
Purchase #4	$165.47	5.297%	$174.2349	$174.23	$174.25	$174.20
Purchase #5	$144.83	9.714%	$158.8988	$158.90	$158.90	$158.90
Purchase #6	$33.41	10.726%	$36.9936	$36.99	$37.00	$37.00
Purchase #7	$243.37	7.526%	$261.686	$261.69	$261.70	$261.70
7 purchase totals =	$832.38		$902.8995	$902.90	$902.95	$902.90