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 $44.80   13.229%   $50.7266   $50.73   $50.75   $50.70  
  Purchase #2 $226.64   10.547%   $250.5437   $250.54   $250.55   $250.50  
  Purchase #3 $36.68   5.449%   $38.6787   $38.68   $38.70   $38.70  
  Purchase #4 $73.46   6.576%   $78.2907   $78.29   $78.30   $78.30  
  Purchase #5 $236.95   10.546%   $261.9387   $261.94   $261.95   $261.90  
  Purchase #6 $164.54   7.446%   $176.7916   $176.79   $176.80   $176.80  
  Purchase #7 $150.75   4.535%   $157.5865   $157.59   $157.60   $157.60  
  7 purchase totals = $933.82       $1,014.5565   $1,014.56   $1,014.65   $1,014.50