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 $68.82   11.544%   $76.7646   $76.76   $76.75   $76.80  
  Purchase #2 $78.46   12.630%   $88.3695   $88.37   $88.35   $88.40  
  Purchase #3 $162.89   6.736%   $173.8623   $173.86   $173.85   $173.90  
  Purchase #4 $10.92   5.737%   $11.5465   $11.55   $11.55   $11.50  
  Purchase #5 $214.85   6.469%   $228.7486   $228.75   $228.75   $228.70  
  Purchase #6 $73.29   12.850%   $82.7078   $82.71   $82.70   $82.70  
  Purchase #7 $165.95   7.302%   $178.0677   $178.07   $178.05   $178.10  
  7 purchase totals = $775.18       $840.0670   $840.07   $840.00   $840.10