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	$186.71	6.400%	$198.6594	$198.66	$198.65	$198.70
Purchase #2	$123.61	11.301%	$137.5792	$137.58	$137.60	$137.60
Purchase #3	$51.28	12.854%	$57.8715	$57.87	$57.85	$57.90
Purchase #4	$108.47	6.831%	$115.8796	$115.88	$115.90	$115.90
Purchase #5	$195.68	10.523%	$216.2714	$216.27	$216.25	$216.30
Purchase #6	$151.89	13.599%	$172.5455	$172.55	$172.55	$172.50
Purchase #7	$30.43	3.759%	$31.5739	$31.57	$31.55	$31.60
7 purchase totals =	$848.07		$930.3805	$930.38	$930.35	$930.50