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 $236.28   10.581%   $261.2808   $261.28   $261.30   $261.30  
  Purchase #2 $62.74   7.726%   $67.5873   $67.59   $67.60   $67.60  
  Purchase #3 $5.95   13.381%   $6.7462   $6.75   $6.75   $6.70  
  Purchase #4 $135.53   12.657%   $152.684   $152.68   $152.70   $152.70  
  Purchase #5 $117.54   5.842%   $124.4067   $124.41   $124.40   $124.40  
  Purchase #6 $65.88   7.316%   $70.6998   $70.70   $70.70   $70.70  
  Purchase #7 $76.56   3.714%   $79.4034   $79.40   $79.40   $79.40  
  7 purchase totals = $700.48       $762.8082   $762.81   $762.85   $762.80