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 $208.63   11.813%   $233.2755   $233.28   $233.30   $233.30  
  Purchase #2 $8.38   11.587%   $9.351   $9.35   $9.35   $9.40  
  Purchase #3 $168.45   6.645%   $179.6435   $179.64   $179.65   $179.60  
  Purchase #4 $16.83   6.625%   $17.945   $17.95   $17.95   $17.90  
  Purchase #5 $78.92   3.822%   $81.9363   $81.94   $81.95   $81.90  
  Purchase #6 $192.61   3.787%   $199.9041   $199.90   $199.90   $199.90  
  Purchase #7 $146.90   6.193%   $155.9975   $156.00   $156.00   $156.00  
  7 purchase totals = $820.72       $878.0529   $878.06   $878.10   $878.00