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 $65.97   9.819%   $72.4476   $72.45   $72.45   $72.40  
  Purchase #2 $156.41   6.732%   $166.9395   $166.94   $166.95   $166.90  
  Purchase #3 $45.83   11.376%   $51.0436   $51.04   $51.05   $51.00  
  Purchase #4 $75.45   3.187%   $77.8546   $77.85   $77.85   $77.90  
  Purchase #5 $181.45   9.269%   $198.2686   $198.27   $198.25   $198.30  
  Purchase #6 $242.75   4.195%   $252.9334   $252.93   $252.95   $252.90  
  Purchase #7 $82.86   3.730%   $85.9507   $85.95   $85.95   $86.00  
  7 purchase totals = $850.72       $905.4380   $905.43   $905.45   $905.40