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 $177.65   12.723%   $200.2524   $200.25   $200.25   $200.30  
  Purchase #2 $209.48   3.464%   $216.7364   $216.74   $216.75   $216.70  
  Purchase #3 $80.69   3.482%   $83.4996   $83.50   $83.50   $83.50  
  Purchase #4 $239.58   9.720%   $262.8672   $262.87   $262.85   $262.90  
  Purchase #5 $29.47   13.472%   $33.4402   $33.44   $33.45   $33.40  
  Purchase #6 $160.81   8.504%   $174.4853   $174.49   $174.50   $174.50  
  Purchase #7 $46.66   8.665%   $50.7031   $50.70   $50.70   $50.70  
  7 purchase totals = $944.34       $1,021.9842   $1,021.99   $1,022.00   $1,022.00