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	$132.42	5.807%	$140.1096	$140.11	$140.10	$140.10
Purchase #2	$163.60	11.779%	$182.8704	$182.87	$182.85	$182.90
Purchase #3	$104.81	3.626%	$108.6104	$108.61	$108.60	$108.60
Purchase #4	$127.50	12.321%	$143.2093	$143.21	$143.20	$143.20
Purchase #5	$112.36	4.825%	$117.7814	$117.78	$117.80	$117.80
Purchase #6	$82.55	11.245%	$91.8327	$91.83	$91.85	$91.80
Purchase #7	$44.65	12.295%	$50.1397	$50.14	$50.15	$50.10
7 purchase totals =	$767.89		$834.5535	$834.55	$834.55	$834.50