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	$81.85	8.534%	$88.8351	$88.84	$88.85	$88.80
Purchase #2	$224.94	12.679%	$253.4601	$253.46	$253.45	$253.50
Purchase #3	$80.52	10.555%	$89.0189	$89.02	$89.00	$89.00
Purchase #4	$171.69	9.144%	$187.3893	$187.39	$187.40	$187.40
Purchase #5	$87.46	6.190%	$92.8738	$92.87	$92.85	$92.90
Purchase #6	$120.32	5.509%	$126.9484	$126.95	$126.95	$126.90
Purchase #7	$163.82	11.646%	$182.8985	$182.90	$182.90	$182.90
7 purchase totals =	$930.60		$1,021.4241	$1,021.43	$1,021.40	$1,021.40