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 $66.61   4.564%   $69.6501   $69.65   $69.65   $69.70  
  Purchase #2 $115.65   8.438%   $125.4085   $125.41   $125.40   $125.40  
  Purchase #3 $165.70   7.791%   $178.6097   $178.61   $178.60   $178.60  
  Purchase #4 $245.31   7.826%   $264.508   $264.51   $264.50   $264.50  
  Purchase #5 $58.33   4.697%   $61.0698   $61.07   $61.05   $61.10  
  Purchase #6 $132.73   11.251%   $147.6635   $147.66   $147.65   $147.70  
  Purchase #7 $36.76   11.193%   $40.8745   $40.87   $40.85   $40.90  
  7 purchase totals = $821.09       $887.7841   $887.78   $887.70   $887.90