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 $78.28   10.198%   $86.263   $86.26   $86.25   $86.30  
  Purchase #2 $50.47   3.498%   $52.2354   $52.24   $52.25   $52.20  
  Purchase #3 $42.99   11.614%   $47.9829   $47.98   $48.00   $48.00  
  Purchase #4 $229.75   3.161%   $237.0124   $237.01   $237.00   $237.00  
  Purchase #5 $192.79   6.297%   $204.93   $204.93   $204.95   $204.90  
  Purchase #6 $224.31   13.774%   $255.2065   $255.21   $255.20   $255.20  
  Purchase #7 $130.64   11.695%   $145.9183   $145.92   $145.90   $145.90  
  7 purchase totals = $949.23       $1,029.5485   $1,029.55   $1,029.55   $1,029.50