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 $83.76   11.833%   $93.6713   $93.67   $93.65   $93.70  
  Purchase #2 $239.83   3.343%   $247.8475   $247.85   $247.85   $247.80  
  Purchase #3 $86.59   9.484%   $94.8022   $94.80   $94.80   $94.80  
  Purchase #4 $154.84   12.751%   $174.5836   $174.58   $174.60   $174.60  
  Purchase #5 $146.61   5.228%   $154.2748   $154.27   $154.25   $154.30  
  Purchase #6 $168.59   6.838%   $180.1182   $180.12   $180.10   $180.10  
  Purchase #7 $42.78   8.775%   $46.5339   $46.53   $46.55   $46.50  
  7 purchase totals = $923.00       $991.8315   $991.82   $991.80   $991.80