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	$28.36	11.426%	$31.6004	$31.60	$31.60	$31.60
Purchase #2	$85.67	11.416%	$95.4501	$95.45	$95.45	$95.50
Purchase #3	$217.33	12.479%	$244.4506	$244.45	$244.45	$244.50
Purchase #4	$163.87	10.343%	$180.8191	$180.82	$180.80	$180.80
Purchase #5	$88.29	13.555%	$100.2577	$100.26	$100.25	$100.30
Purchase #6	$85.53	13.816%	$97.3468	$97.35	$97.35	$97.30
Purchase #7	$170.27	13.334%	$192.9738	$192.97	$192.95	$193.00
7 purchase totals =	$839.32		$942.8985	$942.90	$942.85	$943.00