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	$205.92	6.298%	$218.8888	$218.89	$218.90	$218.90
Purchase #2	$31.89	12.465%	$35.8651	$35.87	$35.85	$35.90
Purchase #3	$29.49	9.379%	$32.2559	$32.26	$32.25	$32.30
Purchase #4	$144.87	5.835%	$153.3232	$153.32	$153.30	$153.30
Purchase #5	$179.88	11.669%	$200.8702	$200.87	$200.85	$200.90
Purchase #6	$153.88	11.235%	$171.1684	$171.17	$171.15	$171.20
Purchase #7	$104.37	8.742%	$113.494	$113.49	$113.50	$113.50
7 purchase totals =	$850.30		$925.8656	$925.87	$925.80	$926.00