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 $239.95   8.155%   $259.5179   $259.52   $259.50   $259.50  
  Purchase #2 $10.58   10.203%   $11.6595   $11.66   $11.65   $11.70  
  Purchase #3 $52.50   6.104%   $55.7046   $55.70   $55.70   $55.70  
  Purchase #4 $147.93   7.385%   $158.8546   $158.85   $158.85   $158.90  
  Purchase #5 $195.56   11.521%   $218.0905   $218.09   $218.10   $218.10  
  Purchase #6 $22.58   9.719%   $24.7746   $24.77   $24.75   $24.80  
  Purchase #7 $208.54   5.621%   $220.262   $220.26   $220.25   $220.30  
  7 purchase totals = $877.64       $948.8637   $948.85   $948.80   $949.00