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	$63.50	5.701%	$67.1201	$67.12	$67.10	$67.10
Purchase #2	$208.53	5.392%	$219.7739	$219.77	$219.75	$219.80
Purchase #3	$140.88	13.262%	$159.5635	$159.56	$159.55	$159.60
Purchase #4	$113.57	8.521%	$123.2473	$123.25	$123.25	$123.20
Purchase #5	$19.27	6.676%	$20.5565	$20.56	$20.55	$20.60
Purchase #6	$250.36	11.491%	$279.1289	$279.13	$279.15	$279.10
Purchase #7	$118.67	7.795%	$127.9203	$127.92	$127.90	$127.90
7 purchase totals =	$914.78		$997.3105	$997.31	$997.25	$997.30