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	$9.86	3.166%	$10.1722	$10.17	$10.15	$10.20
Purchase #2	$135.87	4.730%	$142.2967	$142.30	$142.30	$142.30
Purchase #3	$162.80	6.778%	$173.8346	$173.83	$173.85	$173.80
Purchase #4	$87.73	13.236%	$99.3419	$99.34	$99.35	$99.30
Purchase #5	$140.94	4.170%	$146.8172	$146.82	$146.80	$146.80
Purchase #6	$87.64	10.680%	$97	$97.00	$97.00	$97.00
Purchase #7	$238.55	8.352%	$258.4737	$258.47	$258.45	$258.50
7 purchase totals =	$863.39		$927.9363	$927.93	$927.90	$927.90