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 $244.25   5.695%   $258.16   $258.16   $258.15   $258.20  
  Purchase #2 $58.32   9.292%   $63.7391   $63.74   $63.75   $63.70  
  Purchase #3 $52.70   5.226%   $55.4541   $55.45   $55.45   $55.50  
  Purchase #4 $34.94   6.612%   $37.2502   $37.25   $37.25   $37.30  
  Purchase #5 $49.31   4.697%   $51.6261   $51.63   $51.65   $51.60  
  Purchase #6 $12.76   5.202%   $13.4238   $13.42   $13.40   $13.40  
  Purchase #7 $74.84   13.587%   $85.0085   $85.01   $85.00   $85.00  
  7 purchase totals = $527.12       $564.6618   $564.66   $564.65   $564.70