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 $23.87   3.168%   $24.6262   $24.63   $24.65   $24.60  
  Purchase #2 $118.25   7.260%   $126.835   $126.84   $126.85   $126.80  
  Purchase #3 $30.76   9.574%   $33.705   $33.71   $33.70   $33.70  
  Purchase #4 $142.43   11.580%   $158.9234   $158.92   $158.90   $158.90  
  Purchase #5 $167.90   3.637%   $174.0065   $174.01   $174.00   $174.00  
  Purchase #6 $15.39   13.577%   $17.4795   $17.48   $17.50   $17.50  
  Purchase #7 $201.97   12.636%   $227.4909   $227.49   $227.50   $227.50  
  7 purchase totals = $700.57       $763.0665   $763.08   $763.10   $763.00