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 $69.32   11.458%   $77.2627   $77.26   $77.25   $77.30  
  Purchase #2 $183.33   12.551%   $206.3397   $206.34   $206.35   $206.30  
  Purchase #3 $118.97   6.549%   $126.7613   $126.76   $126.75   $126.80  
  Purchase #4 $215.52   10.126%   $237.3436   $237.34   $237.35   $237.30  
  Purchase #5 $148.63   13.799%   $169.1395   $169.14   $169.15   $169.10  
  Purchase #6 $149.68   5.643%   $158.1264   $158.13   $158.15   $158.10  
  Purchase #7 $232.34   12.713%   $261.8774   $261.88   $261.90   $261.90  
  7 purchase totals = $1,117.79       $1,236.8506   $1,236.85   $1,236.90   $1,236.80