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 $58.29   8.116%   $63.0208   $63.02   $63.00   $63.00  
  Purchase #2 $161.26   7.657%   $173.6077   $173.61   $173.60   $173.60  
  Purchase #3 $71.65   3.465%   $74.1327   $74.13   $74.15   $74.10  
  Purchase #4 $29.63   4.246%   $30.8881   $30.89   $30.90   $30.90  
  Purchase #5 $218.69   8.800%   $237.9347   $237.93   $237.95   $237.90  
  Purchase #6 $202.45   12.603%   $227.9648   $227.96   $227.95   $228.00  
  Purchase #7 $30.77   13.787%   $35.0123   $35.01   $35.00   $35.00  
  7 purchase totals = $772.74       $842.5611   $842.55   $842.55   $842.50