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	$40.76	3.709%	$42.2718	$42.27	$42.25	$42.30
Purchase #2	$95.69	8.835%	$104.1442	$104.14	$104.15	$104.10
Purchase #3	$36.76	4.361%	$38.3631	$38.36	$38.35	$38.40
Purchase #4	$221.61	4.591%	$231.7841	$231.78	$231.80	$231.80
Purchase #5	$86.33	4.186%	$89.9438	$89.94	$89.95	$89.90
Purchase #6	$10.38	5.751%	$10.977	$10.98	$11.00	$11.00
Purchase #7	$114.87	5.347%	$121.0121	$121.01	$121.00	$121.00
7 purchase totals =	$606.40		$638.4961	$638.48	$638.50	$638.50