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 $81.74   13.692%   $92.9318   $92.93   $92.95   $92.90  
  Purchase #2 $14.55   8.149%   $15.7357   $15.74   $15.75   $15.70  
  Purchase #3 $179.51   5.183%   $188.814   $188.81   $188.80   $188.80  
  Purchase #4 $187.58   3.149%   $193.4869   $193.49   $193.50   $193.50  
  Purchase #5 $190.42   7.561%   $204.8177   $204.82   $204.80   $204.80  
  Purchase #6 $145.48   4.425%   $151.9175   $151.92   $151.90   $151.90  
  Purchase #7 $187.75   10.811%   $208.0477   $208.05   $208.05   $208.00  
  7 purchase totals = $987.03       $1,055.7513   $1,055.76   $1,055.75   $1,055.60