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 $22.54   12.689%   $25.4001   $25.40   $25.40   $25.40  
  Purchase #2 $226.97   13.507%   $257.6268   $257.63   $257.65   $257.60  
  Purchase #3 $243.28   6.436%   $258.9375   $258.94   $258.95   $258.90  
  Purchase #4 $53.85   13.160%   $60.9367   $60.94   $60.95   $60.90  
  Purchase #5 $136.58   7.244%   $146.4739   $146.47   $146.45   $146.50  
  Purchase #6 $202.25   10.240%   $222.9604   $222.96   $222.95   $223.00  
  Purchase #7 $131.85   8.189%   $142.6472   $142.65   $142.65   $142.60  
  7 purchase totals = $1,017.32       $1,114.9826   $1,114.99   $1,115.00   $1,114.90