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 $191.87   3.678%   $198.927   $198.93   $198.95   $198.90  
  Purchase #2 $235.55   12.853%   $265.8252   $265.83   $265.85   $265.80  
  Purchase #3 $233.86   4.564%   $244.5334   $244.53   $244.55   $244.50  
  Purchase #4 $29.64   3.190%   $30.5855   $30.59   $30.60   $30.60  
  Purchase #5 $17.25   13.380%   $19.5581   $19.56   $19.55   $19.60  
  Purchase #6 $19.44   8.840%   $21.1585   $21.16   $21.15   $21.20  
  Purchase #7 $27.60   12.625%   $31.0845   $31.08   $31.10   $31.10  
  7 purchase totals = $755.21       $811.6722   $811.68   $811.75   $811.70