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 $236.30   3.115%   $243.6607   $243.66   $243.65   $243.70  
  Purchase #2 $177.80   7.869%   $191.7911   $191.79   $191.80   $191.80  
  Purchase #3 $140.63   9.109%   $153.44   $153.44   $153.45   $153.40  
  Purchase #4 $23.56   12.289%   $26.4553   $26.46   $26.45   $26.50  
  Purchase #5 $16.43   6.808%   $17.5486   $17.55   $17.55   $17.50  
  Purchase #6 $156.40   11.798%   $174.8521   $174.85   $174.85   $174.90  
  Purchase #7 $232.95   11.611%   $259.9978   $260.00   $260.00   $260.00  
  7 purchase totals = $984.07       $1,067.7456   $1,067.75   $1,067.75   $1,067.80