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 $57.58   6.864%   $61.5323   $61.53   $61.55   $61.50  
  Purchase #2 $73.33   4.386%   $76.5463   $76.55   $76.55   $76.50  
  Purchase #3 $35.67   3.183%   $36.8054   $36.81   $36.80   $36.80  
  Purchase #4 $59.31   6.465%   $63.1444   $63.14   $63.15   $63.10  
  Purchase #5 $183.69   10.499%   $202.9756   $202.98   $203.00   $203.00  
  Purchase #6 $94.88   5.109%   $99.7274   $99.73   $99.75   $99.70  
  Purchase #7 $14.47   8.623%   $15.7177   $15.72   $15.70   $15.70  
  7 purchase totals = $518.93       $556.4491   $556.46   $556.50   $556.30