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 $144.95   6.423%   $154.2601   $154.26   $154.25   $154.30  
  Purchase #2 $73.87   8.223%   $79.9443   $79.94   $79.95   $79.90  
  Purchase #3 $11.87   7.574%   $12.769   $12.77   $12.75   $12.80  
  Purchase #4 $21.84   9.490%   $23.9126   $23.91   $23.90   $23.90  
  Purchase #5 $226.66   8.506%   $245.9397   $245.94   $245.95   $245.90  
  Purchase #6 $59.59   11.278%   $66.3106   $66.31   $66.30   $66.30  
  Purchase #7 $200.44   4.711%   $209.8827   $209.88   $209.90   $209.90  
  7 purchase totals = $739.22       $793.0190   $793.01   $793.00   $793.00