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 $201.73   12.523%   $226.9926   $226.99   $227.00   $227.00  
  Purchase #2 $34.56   13.770%   $39.3189   $39.32   $39.30   $39.30  
  Purchase #3 $25.39   5.731%   $26.8451   $26.85   $26.85   $26.80  
  Purchase #4 $93.95   6.623%   $100.1723   $100.17   $100.15   $100.20  
  Purchase #5 $191.49   4.436%   $199.9845   $199.98   $200.00   $200.00  
  Purchase #6 $163.75   11.677%   $182.8711   $182.87   $182.85   $182.90  
  Purchase #7 $226.41   3.768%   $234.9411   $234.94   $234.95   $234.90  
  7 purchase totals = $937.28       $1,011.1256   $1,011.12   $1,011.10   $1,011.10