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 $113.27   11.656%   $126.4728   $126.47   $126.45   $126.50  
  Purchase #2 $213.34   9.828%   $234.3071   $234.31   $234.30   $234.30  
  Purchase #3 $55.92   7.774%   $60.2672   $60.27   $60.25   $60.30  
  Purchase #4 $114.35   3.709%   $118.5912   $118.59   $118.60   $118.60  
  Purchase #5 $29.57   3.592%   $30.6322   $30.63   $30.65   $30.60  
  Purchase #6 $175.73   7.459%   $188.8377   $188.84   $188.85   $188.80  
  Purchase #7 $35.88   11.292%   $39.9316   $39.93   $39.95   $39.90  
  7 purchase totals = $738.06       $799.0398   $799.04   $799.05   $799.00