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 $34.95   10.304%   $38.5512   $38.55   $38.55   $38.60  
  Purchase #2 $230.64   12.331%   $259.0802   $259.08   $259.10   $259.10  
  Purchase #3 $49.83   9.555%   $54.5913   $54.59   $54.60   $54.60  
  Purchase #4 $103.86   3.703%   $107.7059   $107.71   $107.70   $107.70  
  Purchase #5 $9.31   5.147%   $9.7892   $9.79   $9.80   $9.80  
  Purchase #6 $146.26   11.228%   $162.6821   $162.68   $162.70   $162.70  
  Purchase #7 $231.64   8.136%   $250.4862   $250.49   $250.50   $250.50  
  7 purchase totals = $806.49       $882.8861   $882.89   $882.95   $883.00