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	$29.42	7.186%	$31.5341	$31.53	$31.55	$31.50
Purchase #2	$45.47	4.562%	$47.5443	$47.54	$47.55	$47.50
Purchase #3	$67.60	5.853%	$71.5566	$71.56	$71.55	$71.60
Purchase #4	$127.67	9.310%	$139.5561	$139.56	$139.55	$139.60
Purchase #5	$18.56	7.147%	$19.8865	$19.89	$19.90	$19.90
Purchase #6	$195.53	6.193%	$207.6392	$207.64	$207.65	$207.60
Purchase #7	$118.57	5.308%	$124.8637	$124.86	$124.85	$124.90
7 purchase totals =	$602.82		$642.5805	$642.58	$642.60	$642.60