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 $242.57   10.737%   $268.6147   $268.61   $268.60   $268.60  
  Purchase #2 $97.70   6.519%   $104.0691   $104.07   $104.05   $104.10  
  Purchase #3 $22.75   13.654%   $25.8563   $25.86   $25.85   $25.90  
  Purchase #4 $226.37   11.839%   $253.1699   $253.17   $253.15   $253.20  
  Purchase #5 $17.76   12.265%   $19.9383   $19.94   $19.95   $19.90  
  Purchase #6 $248.80   10.665%   $275.3345   $275.33   $275.35   $275.30  
  Purchase #7 $112.80   6.441%   $120.0654   $120.07   $120.05   $120.10  
  7 purchase totals = $968.75       $1,067.0482   $1,067.05   $1,067.00   $1,067.10