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 $145.88   8.269%   $157.9428   $157.94   $157.95   $157.90  
  Purchase #2 $171.79   11.523%   $191.5854   $191.59   $191.60   $191.60  
  Purchase #3 $183.87   13.645%   $208.9591   $208.96   $208.95   $209.00  
  Purchase #4 $57.70   12.520%   $64.924   $64.92   $64.90   $64.90  
  Purchase #5 $182.57   13.588%   $207.3776   $207.38   $207.40   $207.40  
  Purchase #6 $177.92   10.287%   $196.2226   $196.22   $196.20   $196.20  
  Purchase #7 $24.44   6.706%   $26.0789   $26.08   $26.10   $26.10  
  7 purchase totals = $944.17       $1,053.0904   $1,053.09   $1,053.10   $1,053.10