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 $23.54   8.413%   $25.5204   $25.52   $25.50   $25.50  
  Purchase #2 $202.34   3.816%   $210.0613   $210.06   $210.05   $210.10  
  Purchase #3 $241.50   8.159%   $261.204   $261.20   $261.20   $261.20  
  Purchase #4 $56.97   4.418%   $59.4869   $59.49   $59.50   $59.50  
  Purchase #5 $10.89   4.586%   $11.3894   $11.39   $11.40   $11.40  
  Purchase #6 $171.61   9.366%   $187.683   $187.68   $187.70   $187.70  
  Purchase #7 $143.94   8.465%   $156.1245   $156.12   $156.10   $156.10  
  7 purchase totals = $850.79       $911.4695   $911.46   $911.45   $911.50