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	$126.75	8.811%	$137.9179	$137.92	$137.90	$137.90
Purchase #2	$82.98	11.182%	$92.2588	$92.26	$92.25	$92.30
Purchase #3	$237.57	9.142%	$259.2886	$259.29	$259.30	$259.30
Purchase #4	$196.53	11.159%	$218.4608	$218.46	$218.45	$218.50
Purchase #5	$214.60	12.146%	$240.6653	$240.67	$240.65	$240.70
Purchase #6	$78.50	5.339%	$82.6911	$82.69	$82.70	$82.70
Purchase #7	$124.97	11.286%	$139.0741	$139.07	$139.05	$139.10
7 purchase totals =	$1,061.90		$1,170.3566	$1,170.36	$1,170.30	$1,170.50