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 $183.79   13.696%   $208.9619   $208.96   $208.95   $209.00  
  Purchase #2 $187.72   8.286%   $203.2745   $203.27   $203.25   $203.30  
  Purchase #3 $174.54   12.113%   $195.682   $195.68   $195.70   $195.70  
  Purchase #4 $31.76   7.696%   $34.2042   $34.20   $34.20   $34.20  
  Purchase #5 $210.41   13.815%   $239.4781   $239.48   $239.50   $239.50  
  Purchase #6 $119.50   6.230%   $126.9449   $126.94   $126.95   $126.90  
  Purchase #7 $89.55   3.124%   $92.3475   $92.35   $92.35   $92.30  
  7 purchase totals = $997.27       $1,100.8931   $1,100.88   $1,100.90   $1,100.90