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 $47.62   3.308%   $49.1953   $49.20   $49.20   $49.20  
  Purchase #2 $136.99   11.464%   $152.6945   $152.69   $152.70   $152.70  
  Purchase #3 $119.45   5.214%   $125.6781   $125.68   $125.70   $125.70  
  Purchase #4 $213.76   12.291%   $240.0332   $240.03   $240.05   $240.00  
  Purchase #5 $130.26   3.807%   $135.219   $135.22   $135.20   $135.20  
  Purchase #6 $65.56   10.854%   $72.6759   $72.68   $72.70   $72.70  
  Purchase #7 $24.80   7.396%   $26.6342   $26.63   $26.65   $26.60  
  7 purchase totals = $738.44       $802.1302   $802.13   $802.20   $802.10