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 $245.27   6.872%   $262.125   $262.13   $262.15   $262.10  
  Purchase #2 $106.84   5.416%   $112.6265   $112.63   $112.65   $112.60  
  Purchase #3 $44.44   8.115%   $48.0463   $48.05   $48.05   $48.00  
  Purchase #4 $126.98   8.868%   $138.2406   $138.24   $138.25   $138.20  
  Purchase #5 $193.73   13.757%   $220.3814   $220.38   $220.40   $220.40  
  Purchase #6 $24.31   8.437%   $26.361   $26.36   $26.35   $26.40  
  Purchase #7 $248.31   9.354%   $271.5369   $271.54   $271.55   $271.50  
  7 purchase totals = $989.88       $1,079.3177   $1,079.33   $1,079.40   $1,079.20