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 $245.27   6.412%   $260.9967   $261.00   $261.00   $261.00  
  Purchase #2 $246.60   5.840%   $261.0014   $261.00   $261.00   $261.00  
  Purchase #3 $161.72   6.315%   $171.9326   $171.93   $171.95   $171.90  
  Purchase #4 $76.64   7.658%   $82.5091   $82.51   $82.50   $82.50  
  Purchase #5 $212.52   12.284%   $238.626   $238.63   $238.65   $238.60  
  Purchase #6 $123.47   9.422%   $135.1033   $135.10   $135.10   $135.10  
  Purchase #7 $56.61   3.258%   $58.4544   $58.45   $58.45   $58.50  
  7 purchase totals = $1,122.83       $1,208.6235   $1,208.62   $1,208.65   $1,208.60