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 $248.87   5.548%   $262.6773   $262.68   $262.70   $262.70  
  Purchase #2 $56.78   6.134%   $60.2629   $60.26   $60.25   $60.30  
  Purchase #3 $227.52   13.636%   $258.5446   $258.54   $258.55   $258.50  
  Purchase #4 $231.66   6.872%   $247.5797   $247.58   $247.60   $247.60  
  Purchase #5 $192.46   13.300%   $218.0572   $218.06   $218.05   $218.10  
  Purchase #6 $75.55   5.616%   $79.7929   $79.79   $79.80   $79.80  
  Purchase #7 $27.74   3.766%   $28.7847   $28.78   $28.80   $28.80  
  7 purchase totals = $1,060.58       $1,155.6993   $1,155.69   $1,155.75   $1,155.80