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 $195.71   5.279%   $206.0415   $206.04   $206.05   $206.00  
  Purchase #2 $25.55   4.795%   $26.7751   $26.78   $26.80   $26.80  
  Purchase #3 $224.39   13.407%   $254.474   $254.47   $254.45   $254.50  
  Purchase #4 $200.69   3.365%   $207.4432   $207.44   $207.45   $207.40  
  Purchase #5 $22.28   7.169%   $23.8773   $23.88   $23.90   $23.90  
  Purchase #6 $65.40   10.808%   $72.4684   $72.47   $72.45   $72.50  
  Purchase #7 $69.31   12.445%   $77.9356   $77.94   $77.95   $77.90  
  7 purchase totals = $803.33       $869.0151   $869.02   $869.05   $869.00