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 $178.25   10.260%   $196.5385   $196.54   $196.55   $196.50  
  Purchase #2 $228.25   9.821%   $250.6664   $250.67   $250.65   $250.70  
  Purchase #3 $12.97   13.805%   $14.7605   $14.76   $14.75   $14.80  
  Purchase #4 $23.42   3.361%   $24.2071   $24.21   $24.20   $24.20  
  Purchase #5 $214.60   7.543%   $230.7873   $230.79   $230.80   $230.80  
  Purchase #6 $232.28   6.248%   $246.7929   $246.79   $246.80   $246.80  
  Purchase #7 $28.89   10.576%   $31.9454   $31.95   $31.95   $31.90  
  7 purchase totals = $918.66       $995.6981   $995.71   $995.70   $995.70