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 $242.92   11.102%   $269.889   $269.89   $269.90   $269.90  
  Purchase #2 $72.58   11.212%   $80.7177   $80.72   $80.70   $80.70  
  Purchase #3 $119.71   3.740%   $124.1872   $124.19   $124.20   $124.20  
  Purchase #4 $241.85   6.352%   $257.2123   $257.21   $257.20   $257.20  
  Purchase #5 $148.28   10.102%   $163.2592   $163.26   $163.25   $163.30  
  Purchase #6 $242.54   8.370%   $262.8406   $262.84   $262.85   $262.80  
  Purchase #7 $217.51   7.504%   $233.832   $233.83   $233.85   $233.80  
  7 purchase totals = $1,285.39       $1,391.9380   $1,391.94   $1,391.95   $1,391.90