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 $52.66   7.423%   $56.569   $56.57   $56.55   $56.60  
  Purchase #2 $9.89   8.182%   $10.6992   $10.70   $10.70   $10.70  
  Purchase #3 $85.63   5.306%   $90.1735   $90.17   $90.15   $90.20  
  Purchase #4 $225.66   7.174%   $241.8488   $241.85   $241.85   $241.80  
  Purchase #5 $232.92   13.616%   $264.6344   $264.63   $264.65   $264.60  
  Purchase #6 $201.29   4.425%   $210.1971   $210.20   $210.20   $210.20  
  Purchase #7 $89.27   3.824%   $92.6837   $92.68   $92.70   $92.70  
  7 purchase totals = $897.32       $966.8057   $966.80   $966.80   $966.80