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 $36.69   6.206%   $38.967   $38.97   $38.95   $39.00  
  Purchase #2 $179.34   9.482%   $196.345   $196.35   $196.35   $196.30  
  Purchase #3 $57.90   3.509%   $59.9317   $59.93   $59.95   $59.90  
  Purchase #4 $110.75   10.371%   $122.2359   $122.24   $122.25   $122.20  
  Purchase #5 $229.47   7.318%   $246.2626   $246.26   $246.25   $246.30  
  Purchase #6 $248.97   13.221%   $281.8863   $281.89   $281.90   $281.90  
  Purchase #7 $121.82   3.378%   $125.9351   $125.94   $125.95   $125.90  
  7 purchase totals = $984.94       $1,071.5636   $1,071.58   $1,071.60   $1,071.50