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 $68.28   12.348%   $76.7112   $76.71   $76.70   $76.70  
  Purchase #2 $95.93   8.210%   $103.8059   $103.81   $103.80   $103.80  
  Purchase #3 $246.88   5.604%   $260.7152   $260.72   $260.70   $260.70  
  Purchase #4 $24.70   10.383%   $27.2646   $27.26   $27.25   $27.30  
  Purchase #5 $232.34   4.554%   $242.9208   $242.92   $242.90   $242.90  
  Purchase #6 $220.50   6.770%   $235.4279   $235.43   $235.45   $235.40  
  Purchase #7 $214.45   11.155%   $238.3719   $238.37   $238.35   $238.40  
  7 purchase totals = $1,103.08       $1,185.2175   $1,185.22   $1,185.15   $1,185.20