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 $23.34   12.828%   $26.3341   $26.33   $26.35   $26.30  
  Purchase #2 $110.33   6.324%   $117.3073   $117.31   $117.30   $117.30  
  Purchase #3 $31.71   9.438%   $34.7028   $34.70   $34.70   $34.70  
  Purchase #4 $160.64   9.660%   $176.1578   $176.16   $176.15   $176.20  
  Purchase #5 $185.34   8.501%   $201.0958   $201.10   $201.10   $201.10  
  Purchase #6 $184.62   3.143%   $190.4226   $190.42   $190.40   $190.40  
  Purchase #7 $43.94   9.194%   $47.9798   $47.98   $48.00   $48.00  
  7 purchase totals = $739.92       $794.0002   $794.00   $794.00   $794.00