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 $133.77   5.446%   $141.0551   $141.06   $141.05   $141.10  
  Purchase #2 $87.57   8.502%   $95.0152   $95.02   $95.00   $95.00  
  Purchase #3 $247.44   13.478%   $280.79   $280.79   $280.80   $280.80  
  Purchase #4 $88.51   13.807%   $100.7306   $100.73   $100.75   $100.70  
  Purchase #5 $249.82   11.118%   $277.595   $277.60   $277.60   $277.60  
  Purchase #6 $22.71   6.326%   $24.1466   $24.15   $24.15   $24.10  
  Purchase #7 $31.54   13.189%   $35.6998   $35.70   $35.70   $35.70  
  7 purchase totals = $861.36       $955.0323   $955.05   $955.05   $955.00