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 $82.81   10.117%   $91.1879   $91.19   $91.20   $91.20  
  Purchase #2 $61.87   12.670%   $69.7089   $69.71   $69.70   $69.70  
  Purchase #3 $165.74   13.460%   $188.0486   $188.05   $188.05   $188.00  
  Purchase #4 $146.92   13.295%   $166.453   $166.45   $166.45   $166.50  
  Purchase #5 $245.27   6.176%   $260.4179   $260.42   $260.40   $260.40  
  Purchase #6 $85.84   10.241%   $94.6309   $94.63   $94.65   $94.60  
  Purchase #7 $28.99   3.560%   $30.022   $30.02   $30.00   $30.00  
  7 purchase totals = $817.44       $900.4692   $900.47   $900.45   $900.40