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 $239.41   8.604%   $260.0088   $260.01   $260.00   $260.00  
  Purchase #2 $135.80   7.851%   $146.4617   $146.46   $146.45   $146.50  
  Purchase #3 $20.25   6.831%   $21.6333   $21.63   $21.65   $21.60  
  Purchase #4 $105.35   6.367%   $112.0576   $112.06   $112.05   $112.10  
  Purchase #5 $67.58   11.589%   $75.4118   $75.41   $75.40   $75.40  
  Purchase #6 $163.65   4.174%   $170.4808   $170.48   $170.50   $170.50  
  Purchase #7 $102.32   8.436%   $110.9517   $110.95   $110.95   $111.00  
  7 purchase totals = $834.36       $897.0057   $897.00   $897.00   $897.10