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 $92.65   12.217%   $103.9691   $103.97   $103.95   $104.00  
  Purchase #2 $201.53   7.684%   $217.0156   $217.02   $217.00   $217.00  
  Purchase #3 $178.46   5.463%   $188.2093   $188.21   $188.20   $188.20  
  Purchase #4 $17.87   11.633%   $19.9488   $19.95   $19.95   $19.90  
  Purchase #5 $74.77   5.645%   $78.9908   $78.99   $79.00   $79.00  
  Purchase #6 $139.68   12.353%   $156.9347   $156.93   $156.95   $156.90  
  Purchase #7 $60.83   6.796%   $64.964   $64.96   $64.95   $65.00  
  7 purchase totals = $765.79       $830.0323   $830.03   $830.00   $830.00