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	$27.35	13.588%	$31.0663	$31.07	$31.05	$31.10
Purchase #2	$218.90	6.637%	$233.4284	$233.43	$233.45	$233.40
Purchase #3	$100.43	13.798%	$114.2873	$114.29	$114.30	$114.30
Purchase #4	$96.36	8.403%	$104.4571	$104.46	$104.45	$104.50
Purchase #5	$108.57	8.369%	$117.6562	$117.66	$117.65	$117.70
Purchase #6	$97.98	13.614%	$111.319	$111.32	$111.30	$111.30
Purchase #7	$38.84	5.483%	$40.9696	$40.97	$40.95	$41.00
7 purchase totals =	$688.43		$753.1839	$753.20	$753.15	$753.30