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	$210.43	11.626%	$234.8946	$234.89	$234.90	$234.90
Purchase #2	$49.63	4.578%	$51.9021	$51.90	$51.90	$51.90
Purchase #3	$223.71	3.517%	$231.5779	$231.58	$231.60	$231.60
Purchase #4	$77.73	7.423%	$83.4999	$83.50	$83.50	$83.50
Purchase #5	$160.52	5.265%	$168.9714	$168.97	$168.95	$169.00
Purchase #6	$176.46	12.391%	$198.3252	$198.33	$198.35	$198.30
Purchase #7	$104.25	6.263%	$110.7792	$110.78	$110.80	$110.80
7 purchase totals =	$1,002.73		$1,079.9503	$1,079.95	$1,080.00	$1,080.00