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 $85.58   10.612%   $94.6617   $94.66   $94.65   $94.70  
  Purchase #2 $32.69   8.338%   $35.4157   $35.42   $35.40   $35.40  
  Purchase #3 $159.75   7.277%   $171.375   $171.38   $171.40   $171.40  
  Purchase #4 $214.59   9.549%   $235.0812   $235.08   $235.10   $235.10  
  Purchase #5 $124.28   10.802%   $137.7047   $137.70   $137.70   $137.70  
  Purchase #6 $82.70   13.226%   $93.6379   $93.64   $93.65   $93.60  
  Purchase #7 $158.95   8.638%   $172.6801   $172.68   $172.70   $172.70  
  7 purchase totals = $858.54       $940.5563   $940.56   $940.60   $940.60