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 $40.76   13.227%   $46.1513   $46.15   $46.15   $46.20  
  Purchase #2 $178.36   8.338%   $193.2317   $193.23   $193.25   $193.20  
  Purchase #3 $150.38   13.469%   $170.6347   $170.63   $170.65   $170.60  
  Purchase #4 $171.99   12.557%   $193.5868   $193.59   $193.60   $193.60  
  Purchase #5 $53.53   5.755%   $56.6107   $56.61   $56.60   $56.60  
  Purchase #6 $115.60   6.782%   $123.44   $123.44   $123.45   $123.40  
  Purchase #7 $169.56   9.717%   $186.0361   $186.04   $186.05   $186.00  
  7 purchase totals = $880.18       $969.6913   $969.69   $969.75   $969.60