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	$126.56	4.199%	$131.8743	$131.87	$131.85	$131.90
Purchase #2	$237.94	12.606%	$267.9347	$267.93	$267.95	$267.90
Purchase #3	$23.25	9.635%	$25.4901	$25.49	$25.50	$25.50
Purchase #4	$224.93	13.726%	$255.8039	$255.80	$255.80	$255.80
Purchase #5	$244.50	10.605%	$270.4292	$270.43	$270.45	$270.40
Purchase #6	$99.62	13.434%	$113.003	$113.00	$113.00	$113.00
Purchase #7	$29.85	5.789%	$31.578	$31.58	$31.60	$31.60
7 purchase totals =	$986.65		$1,096.1132	$1,096.10	$1,096.15	$1,096.10