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 $88.44   5.852%   $93.6155   $93.62   $93.60   $93.60  
  Purchase #2 $186.43   4.433%   $194.6944   $194.69   $194.70   $194.70  
  Purchase #3 $246.75   8.692%   $268.1975   $268.20   $268.20   $268.20  
  Purchase #4 $130.37   9.852%   $143.2141   $143.21   $143.20   $143.20  
  Purchase #5 $22.77   3.723%   $23.6177   $23.62   $23.60   $23.60  
  Purchase #6 $33.25   5.748%   $35.1612   $35.16   $35.15   $35.20  
  Purchase #7 $172.45   3.565%   $178.5978   $178.60   $178.60   $178.60  
  7 purchase totals = $880.46       $937.0982   $937.10   $937.05   $937.10