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 $241.54   10.874%   $267.8051   $267.81   $267.80   $267.80  
  Purchase #2 $67.73   9.239%   $73.9876   $73.99   $74.00   $74.00  
  Purchase #3 $111.79   5.116%   $117.5092   $117.51   $117.50   $117.50  
  Purchase #4 $180.67   4.194%   $188.2473   $188.25   $188.25   $188.20  
  Purchase #5 $42.93   12.214%   $48.1735   $48.17   $48.15   $48.20  
  Purchase #6 $95.99   9.576%   $105.182   $105.18   $105.20   $105.20  
  Purchase #7 $236.93   9.160%   $258.6328   $258.63   $258.65   $258.60  
  7 purchase totals = $977.58       $1,059.5375   $1,059.54   $1,059.55   $1,059.50