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 $23.46   5.335%   $24.7116   $24.71   $24.70   $24.70  
  Purchase #2 $162.50   13.546%   $184.5123   $184.51   $184.50   $184.50  
  Purchase #3 $27.66   4.425%   $28.884   $28.88   $28.90   $28.90  
  Purchase #4 $163.55   11.443%   $182.265   $182.27   $182.25   $182.30  
  Purchase #5 $159.76   4.653%   $167.1936   $167.19   $167.20   $167.20  
  Purchase #6 $22.98   13.305%   $26.0375   $26.04   $26.05   $26.00  
  Purchase #7 $129.49   7.311%   $138.957   $138.96   $138.95   $139.00  
  7 purchase totals = $689.40       $752.5610   $752.56   $752.55   $752.60