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 $176.65   5.313%   $186.0354   $186.04   $186.05   $186.00  
  Purchase #2 $215.74   12.588%   $242.8974   $242.90   $242.90   $242.90  
  Purchase #3 $241.62   6.401%   $257.0861   $257.09   $257.10   $257.10  
  Purchase #4 $146.65   4.595%   $153.3886   $153.39   $153.40   $153.40  
  Purchase #5 $111.94   11.334%   $124.6273   $124.63   $124.65   $124.60  
  Purchase #6 $164.89   11.343%   $183.5935   $183.59   $183.60   $183.60  
  Purchase #7 $207.59   5.246%   $218.4802   $218.48   $218.50   $218.50  
  7 purchase totals = $1,265.08       $1,366.1085   $1,366.12   $1,366.20   $1,366.10