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	$95.39	7.801%	$102.8314	$102.83	$102.85	$102.80
Purchase #2	$174.47	8.632%	$189.5303	$189.53	$189.55	$189.50
Purchase #3	$5.88	9.114%	$6.4159	$6.42	$6.40	$6.40
Purchase #4	$92.74	6.828%	$99.0723	$99.07	$99.05	$99.10
Purchase #5	$203.65	11.638%	$227.3508	$227.35	$227.35	$227.40
Purchase #6	$156.77	10.296%	$172.911	$172.91	$172.90	$172.90
Purchase #7	$76.74	10.802%	$85.0295	$85.03	$85.05	$85.00
7 purchase totals =	$805.64		$883.1412	$883.14	$883.15	$883.10