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 $69.81   12.355%   $78.435   $78.44   $78.45   $78.40  
  Purchase #2 $23.53   12.197%   $26.4   $26.40   $26.40   $26.40  
  Purchase #3 $80.57   5.428%   $84.9433   $84.94   $84.95   $84.90  
  Purchase #4 $249.45   10.661%   $276.0439   $276.04   $276.05   $276.00  
  Purchase #5 $247.43   11.847%   $276.743   $276.74   $276.75   $276.70  
  Purchase #6 $86.99   11.601%   $97.0817   $97.08   $97.10   $97.10  
  Purchase #7 $245.67   6.409%   $261.415   $261.42   $261.40   $261.40  
  7 purchase totals = $1,003.45       $1,101.0619   $1,101.06   $1,101.10   $1,100.90