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 $103.48   10.124%   $113.9563   $113.96   $113.95   $114.00  
  Purchase #2 $27.96   7.666%   $30.1034   $30.10   $30.10   $30.10  
  Purchase #3 $227.95   8.645%   $247.6563   $247.66   $247.65   $247.70  
  Purchase #4 $152.51   8.167%   $164.9655   $164.97   $164.95   $165.00  
  Purchase #5 $90.97   3.563%   $94.2113   $94.21   $94.20   $94.20  
  Purchase #6 $247.77   4.345%   $258.5356   $258.54   $258.55   $258.50  
  Purchase #7 $231.48   3.168%   $238.8133   $238.81   $238.80   $238.80  
  7 purchase totals = $1,082.12       $1,148.2417   $1,148.25   $1,148.20   $1,148.30