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	$12.42	8.456%	$13.4702	$13.47	$13.45	$13.50
Purchase #2	$62.63	5.155%	$65.8586	$65.86	$65.85	$65.90
Purchase #3	$187.97	4.655%	$196.72	$196.72	$196.70	$196.70
Purchase #4	$76.31	11.218%	$84.8705	$84.87	$84.85	$84.90
Purchase #5	$29.51	11.258%	$32.8322	$32.83	$32.85	$32.80
Purchase #6	$90.35	11.216%	$100.4837	$100.48	$100.50	$100.50
Purchase #7	$157.49	3.179%	$162.4966	$162.50	$162.50	$162.50
7 purchase totals =	$616.68		$656.7318	$656.73	$656.70	$656.80