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 $176.97   5.255%   $186.2698   $186.27   $186.25   $186.30  
  Purchase #2 $53.93   8.265%   $58.3873   $58.39   $58.40   $58.40  
  Purchase #3 $242.27   3.584%   $250.953   $250.95   $250.95   $251.00  
  Purchase #4 $228.49   5.787%   $241.7127   $241.71   $241.70   $241.70  
  Purchase #5 $201.53   12.383%   $226.4855   $226.49   $226.50   $226.50  
  Purchase #6 $54.67   13.551%   $62.0783   $62.08   $62.10   $62.10  
  Purchase #7 $87.31   13.295%   $98.9179   $98.92   $98.90   $98.90  
  7 purchase totals = $1,045.17       $1,124.8045   $1,124.81   $1,124.80   $1,124.90