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 $23.34   12.245%   $26.198   $26.20   $26.20   $26.20  
  Purchase #2 $38.61   11.298%   $42.9722   $42.97   $42.95   $43.00  
  Purchase #3 $50.43   13.409%   $57.1922   $57.19   $57.20   $57.20  
  Purchase #4 $12.85   13.433%   $14.5761   $14.58   $14.60   $14.60  
  Purchase #5 $150.74   3.855%   $156.551   $156.55   $156.55   $156.60  
  Purchase #6 $43.63   8.543%   $47.3573   $47.36   $47.35   $47.40  
  Purchase #7 $5.31   12.223%   $5.959   $5.96   $5.95   $6.00  
  7 purchase totals = $324.91       $350.8058   $350.81   $350.80   $351.00