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 $241.29   6.710%   $257.4806   $257.48   $257.50   $257.50  
  Purchase #2 $14.71   13.848%   $16.747   $16.75   $16.75   $16.70  
  Purchase #3 $72.61   12.552%   $81.724   $81.72   $81.70   $81.70  
  Purchase #4 $139.47   11.799%   $155.9261   $155.93   $155.95   $155.90  
  Purchase #5 $167.96   9.174%   $183.3687   $183.37   $183.35   $183.40  
  Purchase #6 $127.85   11.508%   $142.563   $142.56   $142.55   $142.60  
  Purchase #7 $221.76   3.706%   $229.9784   $229.98   $230.00   $230.00  
  7 purchase totals = $985.65       $1,067.7878   $1,067.79   $1,067.80   $1,067.80