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 $47.93   11.511%   $53.4472   $53.45   $53.45   $53.40  
  Purchase #2 $97.95   13.273%   $110.9509   $110.95   $110.95   $111.00  
  Purchase #3 $141.69   7.338%   $152.0872   $152.09   $152.10   $152.10  
  Purchase #4 $160.68   10.520%   $177.5835   $177.58   $177.60   $177.60  
  Purchase #5 $134.51   10.409%   $148.5111   $148.51   $148.50   $148.50  
  Purchase #6 $205.54   11.269%   $228.7023   $228.70   $228.70   $228.70  
  Purchase #7 $81.80   7.227%   $87.7117   $87.71   $87.70   $87.70  
  7 purchase totals = $870.10       $958.9939   $958.99   $959.00   $959.00