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 $162.76   6.347%   $173.0904   $173.09   $173.10   $173.10  
  Purchase #2 $38.66   4.496%   $40.3982   $40.40   $40.40   $40.40  
  Purchase #3 $157.29   5.165%   $165.414   $165.41   $165.40   $165.40  
  Purchase #4 $52.29   6.162%   $55.5121   $55.51   $55.50   $55.50  
  Purchase #5 $216.59   7.441%   $232.7065   $232.71   $232.70   $232.70  
  Purchase #6 $230.41   10.125%   $253.739   $253.74   $253.75   $253.70  
  Purchase #7 $24.66   10.216%   $27.1793   $27.18   $27.20   $27.20  
  7 purchase totals = $882.66       $948.0395   $948.04   $948.05   $948.00