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	$91.80	11.395%	$102.2606	$102.26	$102.25	$102.30
Purchase #2	$85.96	10.787%	$95.2325	$95.23	$95.25	$95.20
Purchase #3	$31.42	6.853%	$33.5732	$33.57	$33.55	$33.60
Purchase #4	$173.45	9.678%	$190.2365	$190.24	$190.25	$190.20
Purchase #5	$20.36	7.439%	$21.8746	$21.87	$21.85	$21.90
Purchase #6	$125.37	13.470%	$142.2573	$142.26	$142.25	$142.30
Purchase #7	$50.32	10.266%	$55.4859	$55.49	$55.50	$55.50
7 purchase totals =	$578.68		$640.9206	$640.92	$640.90	$641.00