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 $236.74   9.651%   $259.5878   $259.59   $259.60   $259.60  
  Purchase #2 $111.56   13.756%   $126.9062   $126.91   $126.90   $126.90  
  Purchase #3 $17.43   11.449%   $19.4256   $19.43   $19.45   $19.40  
  Purchase #4 $10.68   11.296%   $11.8864   $11.89   $11.90   $11.90  
  Purchase #5 $75.48   3.138%   $77.8486   $77.85   $77.85   $77.80  
  Purchase #6 $90.78   6.307%   $96.5055   $96.51   $96.50   $96.50  
  Purchase #7 $209.99   11.703%   $234.5651   $234.57   $234.55   $234.60  
  7 purchase totals = $752.66       $826.7252   $826.75   $826.75   $826.70