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 $161.91   5.105%   $170.1755   $170.18   $170.20   $170.20  
  Purchase #2 $234.76   8.194%   $253.9962   $254.00   $254.00   $254.00  
  Purchase #3 $179.96   7.591%   $193.6208   $193.62   $193.60   $193.60  
  Purchase #4 $57.69   13.711%   $65.5999   $65.60   $65.60   $65.60  
  Purchase #5 $211.44   3.326%   $218.4725   $218.47   $218.45   $218.50  
  Purchase #6 $59.66   8.159%   $64.5277   $64.53   $64.55   $64.50  
  Purchase #7 $138.81   10.270%   $153.0658   $153.07   $153.05   $153.10  
  7 purchase totals = $1,044.23       $1,119.4584   $1,119.47   $1,119.45   $1,119.50