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 $125.98   10.613%   $139.3503   $139.35   $139.35   $139.40  
  Purchase #2 $162.76   4.137%   $169.4934   $169.49   $169.50   $169.50  
  Purchase #3 $219.93   4.159%   $229.0769   $229.08   $229.10   $229.10  
  Purchase #4 $121.46   12.583%   $136.7433   $136.74   $136.75   $136.70  
  Purchase #5 $99.42   13.458%   $112.7999   $112.80   $112.80   $112.80  
  Purchase #6 $201.42   7.379%   $216.2828   $216.28   $216.30   $216.30  
  Purchase #7 $28.38   6.765%   $30.2999   $30.30   $30.30   $30.30  
  7 purchase totals = $959.35       $1,034.0465   $1,034.04   $1,034.10   $1,034.10