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 $119.37   10.692%   $132.133   $132.13   $132.15   $132.10  
  Purchase #2 $60.70   10.238%   $66.9145   $66.91   $66.90   $66.90  
  Purchase #3 $230.48   12.649%   $259.6334   $259.63   $259.65   $259.60  
  Purchase #4 $155.64   7.164%   $166.79   $166.79   $166.80   $166.80  
  Purchase #5 $98.51   12.671%   $110.9922   $110.99   $111.00   $111.00  
  Purchase #6 $177.72   5.223%   $187.0023   $187.00   $187.00   $187.00  
  Purchase #7 $179.51   11.545%   $200.2344   $200.23   $200.25   $200.20  
  7 purchase totals = $1,021.93       $1,123.6998   $1,123.68   $1,123.75   $1,123.60