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 $243.34   7.521%   $261.6416   $261.64   $261.65   $261.60  
  Purchase #2 $249.38   6.259%   $264.9887   $264.99   $265.00   $265.00  
  Purchase #3 $92.86   10.546%   $102.653   $102.65   $102.65   $102.70  
  Purchase #4 $7.53   13.756%   $8.5658   $8.57   $8.55   $8.60  
  Purchase #5 $158.60   11.528%   $176.8834   $176.88   $176.90   $176.90  
  Purchase #6 $96.99   3.456%   $100.342   $100.34   $100.35   $100.30  
  Purchase #7 $10.67   10.661%   $11.8075   $11.81   $11.80   $11.80  
  7 purchase totals = $859.37       $926.8820   $926.88   $926.90   $926.90