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 $119.75   12.402%   $134.6014   $134.60   $134.60   $134.60  
  Purchase #2 $199.50   11.116%   $221.6764   $221.68   $221.70   $221.70  
  Purchase #3 $31.71   9.183%   $34.6219   $34.62   $34.60   $34.60  
  Purchase #4 $217.47   9.209%   $237.4968   $237.50   $237.50   $237.50  
  Purchase #5 $164.71   10.340%   $181.741   $181.74   $181.75   $181.70  
  Purchase #6 $234.44   4.786%   $245.6603   $245.66   $245.65   $245.70  
  Purchase #7 $179.55   5.212%   $188.9081   $188.91   $188.90   $188.90  
  7 purchase totals = $1,147.13       $1,244.7059   $1,244.71   $1,244.70   $1,244.70