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 $194.44   3.837%   $201.9007   $201.90   $201.90   $201.90  
  Purchase #2 $155.62   12.752%   $175.4647   $175.46   $175.45   $175.50  
  Purchase #3 $91.70   6.465%   $97.6284   $97.63   $97.65   $97.60  
  Purchase #4 $94.81   3.873%   $98.482   $98.48   $98.50   $98.50  
  Purchase #5 $165.71   8.124%   $179.1723   $179.17   $179.15   $179.20  
  Purchase #6 $50.84   10.428%   $56.1416   $56.14   $56.15   $56.10  
  Purchase #7 $138.46   9.207%   $151.208   $151.21   $151.20   $151.20  
  7 purchase totals = $891.58       $959.9977   $959.99   $960.00   $960.00