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 $140.79   6.153%   $149.4528   $149.45   $149.45   $149.50  
  Purchase #2 $233.97   10.553%   $258.6609   $258.66   $258.65   $258.70  
  Purchase #3 $63.59   13.856%   $72.401   $72.40   $72.40   $72.40  
  Purchase #4 $147.46   10.309%   $162.6617   $162.66   $162.65   $162.70  
  Purchase #5 $10.38   4.636%   $10.8612   $10.86   $10.85   $10.90  
  Purchase #6 $77.59   11.435%   $86.4624   $86.46   $86.45   $86.50  
  Purchase #7 $202.44   8.756%   $220.1656   $220.17   $220.15   $220.20  
  7 purchase totals = $876.22       $960.6656   $960.66   $960.60   $960.90