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 $68.75   10.632%   $76.0595   $76.06   $76.05   $76.10  
  Purchase #2 $121.72   11.283%   $135.4537   $135.45   $135.45   $135.50  
  Purchase #3 $127.78   6.818%   $136.492   $136.49   $136.50   $136.50  
  Purchase #4 $54.25   4.570%   $56.7292   $56.73   $56.75   $56.70  
  Purchase #5 $223.65   3.798%   $232.1442   $232.14   $232.15   $232.10  
  Purchase #6 $58.34   12.473%   $65.6167   $65.62   $65.60   $65.60  
  Purchase #7 $58.70   12.463%   $66.0158   $66.02   $66.00   $66.00  
  7 purchase totals = $713.19       $768.5111   $768.51   $768.50   $768.50