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	$237.31	12.662%	$267.3582	$267.36	$267.35	$267.40
Purchase #2	$123.58	13.252%	$139.9568	$139.96	$139.95	$140.00
Purchase #3	$203.84	9.812%	$223.8408	$223.84	$223.85	$223.80
Purchase #4	$132.76	9.136%	$144.889	$144.89	$144.90	$144.90
Purchase #5	$99.60	4.155%	$103.7384	$103.74	$103.75	$103.70
Purchase #6	$172.30	10.541%	$190.4621	$190.46	$190.45	$190.50
Purchase #7	$133.68	10.182%	$147.2913	$147.29	$147.30	$147.30
7 purchase totals =	$1,103.07		$1,217.5366	$1,217.54	$1,217.55	$1,217.60