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 $49.49   8.482%   $53.6877   $53.69   $53.70   $53.70  
  Purchase #2 $225.81   8.541%   $245.0964   $245.10   $245.10   $245.10  
  Purchase #3 $112.32   7.421%   $120.6553   $120.66   $120.65   $120.70  
  Purchase #4 $179.85   9.785%   $197.4483   $197.45   $197.45   $197.40  
  Purchase #5 $175.89   13.247%   $199.1901   $199.19   $199.20   $199.20  
  Purchase #6 $15.85   8.311%   $17.1673   $17.17   $17.15   $17.20  
  Purchase #7 $84.56   7.417%   $90.8318   $90.83   $90.85   $90.80  
  7 purchase totals = $843.77       $924.0769   $924.09   $924.10   $924.10