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 $164.88   10.450%   $182.11   $182.11   $182.10   $182.10  
  Purchase #2 $248.63   4.801%   $260.5667   $260.57   $260.55   $260.60  
  Purchase #3 $85.46   11.755%   $95.5058   $95.51   $95.50   $95.50  
  Purchase #4 $242.31   12.153%   $271.7579   $271.76   $271.75   $271.80  
  Purchase #5 $162.54   10.261%   $179.2182   $179.22   $179.20   $179.20  
  Purchase #6 $57.73   4.156%   $60.1293   $60.13   $60.15   $60.10  
  Purchase #7 $177.50   8.284%   $192.2041   $192.20   $192.20   $192.20  
  7 purchase totals = $1,139.05       $1,241.4920   $1,241.50   $1,241.45   $1,241.50