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 $237.86   6.282%   $252.8024   $252.80   $252.80   $252.80  
  Purchase #2 $55.49   8.196%   $60.038   $60.04   $60.05   $60.00  
  Purchase #3 $179.42   7.648%   $193.142   $193.14   $193.15   $193.10  
  Purchase #4 $111.90   11.496%   $124.764   $124.76   $124.75   $124.80  
  Purchase #5 $125.56   8.847%   $136.6683   $136.67   $136.65   $136.70  
  Purchase #6 $117.66   7.285%   $126.2315   $126.23   $126.25   $126.20  
  Purchase #7 $192.71   11.200%   $214.2935   $214.29   $214.30   $214.30  
  7 purchase totals = $1,020.60       $1,107.9397   $1,107.93   $1,107.95   $1,107.90