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 $206.85   12.653%   $233.0227   $233.02   $233.00   $233.00  
  Purchase #2 $24.72   5.690%   $26.1266   $26.13   $26.15   $26.10  
  Purchase #3 $44.70   10.219%   $49.2679   $49.27   $49.25   $49.30  
  Purchase #4 $20.77   7.831%   $22.3965   $22.40   $22.40   $22.40  
  Purchase #5 $117.81   3.630%   $122.0865   $122.09   $122.10   $122.10  
  Purchase #6 $66.93   3.392%   $69.2003   $69.20   $69.20   $69.20  
  Purchase #7 $249.37   10.119%   $274.6038   $274.60   $274.60   $274.60  
  7 purchase totals = $731.15       $796.7043   $796.71   $796.70   $796.70