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	$113.73	8.380%	$123.2606	$123.26	$123.25	$123.30
Purchase #2	$102.85	6.835%	$109.8798	$109.88	$109.90	$109.90
Purchase #3	$33.87	6.313%	$36.0082	$36.01	$36.00	$36.00
Purchase #4	$92.70	3.593%	$96.0307	$96.03	$96.05	$96.00
Purchase #5	$40.71	4.399%	$42.5008	$42.50	$42.50	$42.50
Purchase #6	$31.38	4.421%	$32.7673	$32.77	$32.75	$32.80
Purchase #7	$131.28	5.742%	$138.8181	$138.82	$138.80	$138.80
7 purchase totals =	$546.52		$579.2655	$579.27	$579.25	$579.30