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 $208.61   13.809%   $237.417   $237.42   $237.40   $237.40  
  Purchase #2 $22.33   11.788%   $24.9623   $24.96   $24.95   $25.00  
  Purchase #3 $22.89   9.718%   $25.1145   $25.11   $25.10   $25.10  
  Purchase #4 $37.86   12.135%   $42.4543   $42.45   $42.45   $42.50  
  Purchase #5 $243.63   6.468%   $259.388   $259.39   $259.40   $259.40  
  Purchase #6 $177.54   9.397%   $194.2234   $194.22   $194.20   $194.20  
  Purchase #7 $143.36   5.823%   $151.7079   $151.71   $151.70   $151.70  
  7 purchase totals = $856.22       $935.2674   $935.26   $935.20   $935.30