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 $248.79   5.294%   $261.9609   $261.96   $261.95   $262.00  
  Purchase #2 $89.89   8.851%   $97.8462   $97.85   $97.85   $97.80  
  Purchase #3 $102.60   7.250%   $110.0385   $110.04   $110.05   $110.00  
  Purchase #4 $131.96   5.714%   $139.5002   $139.50   $139.50   $139.50  
  Purchase #5 $201.85   7.205%   $216.3933   $216.39   $216.40   $216.40  
  Purchase #6 $151.42   4.604%   $158.3914   $158.39   $158.40   $158.40  
  Purchase #7 $24.90   3.219%   $25.7015   $25.70   $25.70   $25.70  
  7 purchase totals = $951.41       $1,009.8320   $1,009.83   $1,009.85   $1,009.80