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 $247.73   11.792%   $276.9423   $276.94   $276.95   $276.90  
  Purchase #2 $124.86   7.854%   $134.6665   $134.67   $134.65   $134.70  
  Purchase #3 $34.81   10.162%   $38.3474   $38.35   $38.35   $38.30  
  Purchase #4 $181.83   4.843%   $190.636   $190.64   $190.65   $190.60  
  Purchase #5 $141.83   8.619%   $154.0543   $154.05   $154.05   $154.10  
  Purchase #6 $130.65   4.575%   $136.6272   $136.63   $136.65   $136.60  
  Purchase #7 $187.52   7.626%   $201.8203   $201.82   $201.80   $201.80  
  7 purchase totals = $1,049.23       $1,133.0940   $1,133.10   $1,133.10   $1,133.00