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 $227.97   8.173%   $246.602   $246.60   $246.60   $246.60  
  Purchase #2 $126.98   13.399%   $143.9941   $143.99   $144.00   $144.00  
  Purchase #3 $89.67   4.688%   $93.8737   $93.87   $93.85   $93.90  
  Purchase #4 $182.81   9.524%   $200.2208   $200.22   $200.20   $200.20  
  Purchase #5 $95.65   8.129%   $103.4254   $103.43   $103.45   $103.40  
  Purchase #6 $23.68   11.217%   $26.3362   $26.34   $26.35   $26.30  
  Purchase #7 $134.64   5.646%   $142.2418   $142.24   $142.25   $142.20  
  7 purchase totals = $881.40       $956.6940   $956.69   $956.70   $956.60