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 $239.67   6.192%   $254.5104   $254.51   $254.50   $254.50  
  Purchase #2 $221.33   7.340%   $237.5756   $237.58   $237.60   $237.60  
  Purchase #3 $193.41   3.305%   $199.8022   $199.80   $199.80   $199.80  
  Purchase #4 $120.66   4.617%   $126.2309   $126.23   $126.25   $126.20  
  Purchase #5 $201.38   5.779%   $213.0178   $213.02   $213.00   $213.00  
  Purchase #6 $61.80   8.522%   $67.0666   $67.07   $67.05   $67.10  
  Purchase #7 $60.70   13.653%   $68.9874   $68.99   $69.00   $69.00  
  7 purchase totals = $1,098.95       $1,167.1909   $1,167.20   $1,167.20   $1,167.20