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 $182.90   8.664%   $198.7465   $198.75   $198.75   $198.70  
  Purchase #2 $124.47   7.255%   $133.5003   $133.50   $133.50   $133.50  
  Purchase #3 $56.70   11.112%   $63.0005   $63.00   $63.00   $63.00  
  Purchase #4 $220.91   12.377%   $248.252   $248.25   $248.25   $248.30  
  Purchase #5 $24.91   4.462%   $26.0215   $26.02   $26.00   $26.00  
  Purchase #6 $104.82   5.524%   $110.6103   $110.61   $110.60   $110.60  
  Purchase #7 $68.43   4.540%   $71.5367   $71.54   $71.55   $71.50  
  7 purchase totals = $783.14       $851.6678   $851.67   $851.65   $851.60