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 $241.44   5.387%   $254.4464   $254.45   $254.45   $254.40  
  Purchase #2 $127.50   11.593%   $142.2811   $142.28   $142.30   $142.30  
  Purchase #3 $61.88   13.270%   $70.0915   $70.09   $70.10   $70.10  
  Purchase #4 $35.62   5.445%   $37.5595   $37.56   $37.55   $37.60  
  Purchase #5 $211.29   7.385%   $226.8938   $226.89   $226.90   $226.90  
  Purchase #6 $22.99   5.426%   $24.2374   $24.24   $24.25   $24.20  
  Purchase #7 $57.91   5.265%   $60.959   $60.96   $60.95   $61.00  
  7 purchase totals = $758.63       $816.4687   $816.47   $816.50   $816.50