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	$109.41	8.662%	$118.8871	$118.89	$118.90	$118.90
Purchase #2	$242.40	4.340%	$252.9202	$252.92	$252.90	$252.90
Purchase #3	$132.25	5.771%	$139.8821	$139.88	$139.90	$139.90
Purchase #4	$33.47	13.172%	$37.8787	$37.88	$37.90	$37.90
Purchase #5	$85.51	11.113%	$95.0127	$95.01	$95.00	$95.00
Purchase #6	$40.28	3.119%	$41.5363	$41.54	$41.55	$41.50
Purchase #7	$217.26	12.848%	$245.1736	$245.17	$245.15	$245.20
7 purchase totals =	$860.58		$931.2907	$931.29	$931.30	$931.30