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 $46.92   9.865%   $51.5487   $51.55   $51.55   $51.50  
  Purchase #2 $238.46   7.661%   $256.7284   $256.73   $256.75   $256.70  
  Purchase #3 $207.77   7.774%   $223.922   $223.92   $223.90   $223.90  
  Purchase #4 $248.54   13.412%   $281.8742   $281.87   $281.85   $281.90  
  Purchase #5 $186.89   4.713%   $195.6981   $195.70   $195.70   $195.70  
  Purchase #6 $232.95   8.441%   $252.6133   $252.61   $252.60   $252.60  
  Purchase #7 $9.53   7.681%   $10.262   $10.26   $10.25   $10.30  
  7 purchase totals = $1,171.06       $1,272.6467   $1,272.64   $1,272.60   $1,272.60