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 $249.65   3.829%   $259.2091   $259.21   $259.20   $259.20  
  Purchase #2 $209.81   11.448%   $233.829   $233.83   $233.85   $233.80  
  Purchase #3 $73.38   8.232%   $79.4206   $79.42   $79.40   $79.40  
  Purchase #4 $137.96   10.518%   $152.4706   $152.47   $152.45   $152.50  
  Purchase #5 $158.56   5.174%   $166.7639   $166.76   $166.75   $166.80  
  Purchase #6 $21.79   10.380%   $24.0518   $24.05   $24.05   $24.10  
  Purchase #7 $163.44   6.752%   $174.4755   $174.48   $174.50   $174.50  
  7 purchase totals = $1,014.59       $1,090.2205   $1,090.22   $1,090.20   $1,090.30