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 $53.38   3.710%   $55.3604   $55.36   $55.35   $55.40  
  Purchase #2 $201.61   6.747%   $215.2126   $215.21   $215.20   $215.20  
  Purchase #3 $157.88   13.666%   $179.4559   $179.46   $179.45   $179.50  
  Purchase #4 $22.81   6.376%   $24.2644   $24.26   $24.25   $24.30  
  Purchase #5 $58.71   5.460%   $61.9156   $61.92   $61.90   $61.90  
  Purchase #6 $240.77   9.231%   $262.9955   $263.00   $263.00   $263.00  
  Purchase #7 $200.45   4.222%   $208.913   $208.91   $208.90   $208.90  
  7 purchase totals = $935.61       $1,008.1174   $1,008.12   $1,008.05   $1,008.20