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 $182.75   6.190%   $194.0622   $194.06   $194.05   $194.10  
  Purchase #2 $40.80   5.627%   $43.0958   $43.10   $43.10   $43.10  
  Purchase #3 $130.62   3.105%   $134.6758   $134.68   $134.70   $134.70  
  Purchase #4 $206.33   3.376%   $213.2957   $213.30   $213.30   $213.30  
  Purchase #5 $250.78   11.373%   $279.3012   $279.30   $279.30   $279.30  
  Purchase #6 $103.40   8.429%   $112.1156   $112.12   $112.10   $112.10  
  Purchase #7 $39.66   12.761%   $44.721   $44.72   $44.70   $44.70  
  7 purchase totals = $954.34       $1,021.2673   $1,021.28   $1,021.25   $1,021.30