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 $77.57   6.652%   $82.73   $82.73   $82.75   $82.70  
  Purchase #2 $228.37   13.219%   $258.5582   $258.56   $258.55   $258.60  
  Purchase #3 $250.74   8.825%   $272.8678   $272.87   $272.85   $272.90  
  Purchase #4 $107.42   6.267%   $114.152   $114.15   $114.15   $114.20  
  Purchase #5 $249.85   10.332%   $275.6645   $275.66   $275.65   $275.70  
  Purchase #6 $89.73   12.127%   $100.6116   $100.61   $100.60   $100.60  
  Purchase #7 $24.66   6.503%   $26.2636   $26.26   $26.25   $26.30  
  7 purchase totals = $1,028.34       $1,130.8477   $1,130.84   $1,130.80   $1,131.00