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	$105.53	7.317%	$113.2516	$113.25	$113.25	$113.30
Purchase #2	$198.74	11.153%	$220.9055	$220.91	$220.90	$220.90
Purchase #3	$56.90	5.338%	$59.9373	$59.94	$59.95	$59.90
Purchase #4	$166.71	7.732%	$179.6	$179.60	$179.60	$179.60
Purchase #5	$54.51	8.255%	$59.0098	$59.01	$59.00	$59.00
Purchase #6	$27.60	11.155%	$30.6788	$30.68	$30.70	$30.70
Purchase #7	$7.38	6.411%	$7.8531	$7.85	$7.85	$7.90
7 purchase totals =	$617.37		$671.2361	$671.24	$671.25	$671.30