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 $77.59   10.620%   $85.8301   $85.83   $85.85   $85.80  
  Purchase #2 $185.87   11.131%   $206.5592   $206.56   $206.55   $206.60  
  Purchase #3 $158.94   3.247%   $164.1008   $164.10   $164.10   $164.10  
  Purchase #4 $55.66   5.706%   $58.836   $58.84   $58.85   $58.80  
  Purchase #5 $7.48   7.831%   $8.0658   $8.07   $8.05   $8.10  
  Purchase #6 $191.77   5.488%   $202.2943   $202.29   $202.30   $202.30  
  Purchase #7 $45.75   3.184%   $47.2067   $47.21   $47.20   $47.20  
  7 purchase totals = $723.06       $772.8929   $772.90   $772.90   $772.90