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 $209.56   12.513%   $235.7822   $235.78   $235.80   $235.80  
  Purchase #2 $22.66   10.430%   $25.0234   $25.02   $25.00   $25.00  
  Purchase #3 $213.54   5.208%   $224.6612   $224.66   $224.65   $224.70  
  Purchase #4 $74.95   6.406%   $79.7513   $79.75   $79.75   $79.80  
  Purchase #5 $98.71   6.693%   $105.3167   $105.32   $105.30   $105.30  
  Purchase #6 $61.95   5.718%   $65.4923   $65.49   $65.50   $65.50  
  Purchase #7 $221.41   5.203%   $232.93   $232.93   $232.95   $232.90  
  7 purchase totals = $902.78       $968.9571   $968.95   $968.95   $969.00