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	$209.76	11.811%	$234.5348	$234.53	$234.55	$234.50
Purchase #2	$113.81	5.443%	$120.0047	$120.00	$120.00	$120.00
Purchase #3	$206.89	11.783%	$231.2678	$231.27	$231.25	$231.30
Purchase #4	$232.37	13.136%	$262.8941	$262.89	$262.90	$262.90
Purchase #5	$210.66	6.351%	$224.039	$224.04	$224.05	$224.00
Purchase #6	$152.56	10.671%	$168.8397	$168.84	$168.85	$168.80
Purchase #7	$97.73	6.327%	$103.9134	$103.91	$103.90	$103.90
7 purchase totals =	$1,223.78		$1,345.4935	$1,345.48	$1,345.50	$1,345.40