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 $234.70   11.244%   $261.0897   $261.09   $261.10   $261.10  
  Purchase #2 $250.67   9.724%   $275.0452   $275.05   $275.05   $275.00  
  Purchase #3 $99.66   5.399%   $105.0406   $105.04   $105.05   $105.00  
  Purchase #4 $248.49   11.545%   $277.1782   $277.18   $277.20   $277.20  
  Purchase #5 $119.56   10.276%   $131.846   $131.85   $131.85   $131.80  
  Purchase #6 $120.75   9.552%   $132.284   $132.28   $132.30   $132.30  
  Purchase #7 $178.83   5.131%   $188.0058   $188.01   $188.00   $188.00  
  7 purchase totals = $1,252.66       $1,370.4895   $1,370.50   $1,370.55   $1,370.40