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 $217.29   8.466%   $235.6858   $235.69   $235.70   $235.70  
  Purchase #2 $101.46   11.360%   $112.9859   $112.99   $113.00   $113.00  
  Purchase #3 $30.94   5.850%   $32.75   $32.75   $32.75   $32.80  
  Purchase #4 $162.64   8.553%   $176.5506   $176.55   $176.55   $176.60  
  Purchase #5 $81.50   3.574%   $84.4128   $84.41   $84.40   $84.40  
  Purchase #6 $82.93   12.326%   $93.152   $93.15   $93.15   $93.20  
  Purchase #7 $65.79   5.321%   $69.2907   $69.29   $69.30   $69.30  
  7 purchase totals = $742.55       $804.8278   $804.83   $804.85   $805.00