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	$36.47	9.798%	$40.0433	$40.04	$40.05	$40.00
Purchase #2	$142.46	9.508%	$156.0051	$156.01	$156.00	$156.00
Purchase #3	$65.53	5.558%	$69.1722	$69.17	$69.15	$69.20
Purchase #4	$117.54	9.186%	$128.3372	$128.34	$128.35	$128.30
Purchase #5	$182.95	11.794%	$204.5271	$204.53	$204.55	$204.50
Purchase #6	$96.92	3.766%	$100.57	$100.57	$100.55	$100.60
Purchase #7	$78.89	9.362%	$86.2757	$86.28	$86.30	$86.30
7 purchase totals =	$720.76		$784.9306	$784.94	$784.95	$784.90