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 $23.53   13.788%   $26.7743   $26.77   $26.75   $26.80  
  Purchase #2 $121.94   3.593%   $126.3213   $126.32   $126.30   $126.30  
  Purchase #3 $124.86   6.243%   $132.655   $132.66   $132.65   $132.70  
  Purchase #4 $85.81   4.512%   $89.6817   $89.68   $89.70   $89.70  
  Purchase #5 $221.41   8.363%   $239.9265   $239.93   $239.95   $239.90  
  Purchase #6 $23.47   13.221%   $26.573   $26.57   $26.55   $26.60  
  Purchase #7 $193.71   5.525%   $204.4125   $204.41   $204.40   $204.40  
  7 purchase totals = $794.73       $846.3443   $846.34   $846.30   $846.40