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 $42.38   10.257%   $46.7269   $46.73   $46.75   $46.70  
  Purchase #2 $136.55   10.271%   $150.5751   $150.58   $150.60   $150.60  
  Purchase #3 $186.35   13.539%   $211.5799   $211.58   $211.60   $211.60  
  Purchase #4 $134.79   4.718%   $141.1494   $141.15   $141.15   $141.10  
  Purchase #5 $58.40   6.706%   $62.3163   $62.32   $62.30   $62.30  
  Purchase #6 $214.68   12.725%   $241.998   $242.00   $242.00   $242.00  
  Purchase #7 $23.88   10.389%   $26.3609   $26.36   $26.35   $26.40  
  7 purchase totals = $797.03       $880.7065   $880.72   $880.75   $880.70