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	$106.41	13.562%	$120.8413	$120.84	$120.85	$120.80
Purchase #2	$94.40	6.489%	$100.5256	$100.53	$100.55	$100.50
Purchase #3	$87.52	11.467%	$97.5559	$97.56	$97.55	$97.60
Purchase #4	$103.87	8.591%	$112.7935	$112.79	$112.80	$112.80
Purchase #5	$29.47	5.574%	$31.1127	$31.11	$31.10	$31.10
Purchase #6	$17.92	12.107%	$20.0896	$20.09	$20.10	$20.10
Purchase #7	$101.66	10.795%	$112.6342	$112.63	$112.65	$112.60
7 purchase totals =	$541.25		$595.5528	$595.55	$595.60	$595.50