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	$68.26	3.852%	$70.8894	$70.89	$70.90	$70.90
Purchase #2	$84.91	8.739%	$92.3303	$92.33	$92.35	$92.30
Purchase #3	$187.55	3.706%	$194.5006	$194.50	$194.50	$194.50
Purchase #4	$65.31	3.491%	$67.59	$67.59	$67.60	$67.60
Purchase #5	$249.89	8.679%	$271.578	$271.58	$271.60	$271.60
Purchase #6	$78.29	9.613%	$85.816	$85.82	$85.80	$85.80
Purchase #7	$91.73	11.783%	$102.5385	$102.54	$102.55	$102.50
7 purchase totals =	$825.94		$885.2428	$885.25	$885.30	$885.20