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 $182.57   7.664%   $196.5622   $196.56   $196.55   $196.60  
  Purchase #2 $95.57   9.745%   $104.8833   $104.88   $104.90   $104.90  
  Purchase #3 $29.29   7.795%   $31.5732   $31.57   $31.55   $31.60  
  Purchase #4 $23.32   12.685%   $26.2781   $26.28   $26.30   $26.30  
  Purchase #5 $59.57   8.181%   $64.4434   $64.44   $64.45   $64.40  
  Purchase #6 $111.76   12.670%   $125.92   $125.92   $125.90   $125.90  
  Purchase #7 $122.25   6.310%   $129.964   $129.96   $129.95   $130.00  
  7 purchase totals = $624.33       $679.6242   $679.61   $679.60   $679.70