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	$45.36	12.570%	$51.0618	$51.06	$51.05	$51.10
Purchase #2	$125.90	9.822%	$138.2659	$138.27	$138.25	$138.30
Purchase #3	$102.81	11.306%	$114.4337	$114.43	$114.45	$114.40
Purchase #4	$93.61	4.163%	$97.507	$97.51	$97.50	$97.50
Purchase #5	$136.72	6.710%	$145.8939	$145.89	$145.90	$145.90
Purchase #6	$131.26	10.333%	$144.8231	$144.82	$144.80	$144.80
Purchase #7	$119.62	9.536%	$131.027	$131.03	$131.05	$131.00
7 purchase totals =	$755.28		$823.0124	$823.01	$823.00	$823.00