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	$36.83	13.841%	$41.9276	$41.93	$41.95	$41.90
Purchase #2	$174.56	12.291%	$196.0152	$196.02	$196.00	$196.00
Purchase #3	$83.91	12.614%	$94.4944	$94.49	$94.50	$94.50
Purchase #4	$154.36	10.687%	$170.8565	$170.86	$170.85	$170.90
Purchase #5	$247.61	12.866%	$279.4675	$279.47	$279.45	$279.50
Purchase #6	$139.47	7.748%	$150.2761	$150.28	$150.30	$150.30
Purchase #7	$45.44	13.497%	$51.573	$51.57	$51.55	$51.60
7 purchase totals =	$882.18		$984.6103	$984.62	$984.60	$984.70