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 $209.83   7.604%   $225.7855   $225.79   $225.80   $225.80  
  Purchase #2 $157.94   11.333%   $175.8393   $175.84   $175.85   $175.80  
  Purchase #3 $145.66   6.158%   $154.6297   $154.63   $154.65   $154.60  
  Purchase #4 $250.85   8.189%   $271.3921   $271.39   $271.40   $271.40  
  Purchase #5 $163.51   13.871%   $186.1905   $186.19   $186.20   $186.20  
  Purchase #6 $130.31   3.392%   $134.7301   $134.73   $134.75   $134.70  
  Purchase #7 $5.88   5.868%   $6.225   $6.23   $6.25   $6.20  
  7 purchase totals = $1,063.98       $1,154.7922   $1,154.80   $1,154.90   $1,154.70