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 $84.31   12.309%   $94.6877   $94.69   $94.70   $94.70  
  Purchase #2 $97.99   6.527%   $104.3858   $104.39   $104.40   $104.40  
  Purchase #3 $180.78   5.473%   $190.6741   $190.67   $190.65   $190.70  
  Purchase #4 $24.26   8.140%   $26.2348   $26.23   $26.25   $26.20  
  Purchase #5 $16.44   8.443%   $17.828   $17.83   $17.85   $17.80  
  Purchase #6 $84.31   13.592%   $95.7694   $95.77   $95.75   $95.80  
  Purchase #7 $211.86   12.210%   $237.7281   $237.73   $237.75   $237.70  
  7 purchase totals = $699.95       $767.3079   $767.31   $767.35   $767.30