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 $14.79   11.674%   $16.5166   $16.52   $16.50   $16.50  
  Purchase #2 $219.94   12.296%   $246.9838   $246.98   $247.00   $247.00  
  Purchase #3 $157.63   8.798%   $171.4983   $171.50   $171.50   $171.50  
  Purchase #4 $66.50   11.618%   $74.226   $74.23   $74.25   $74.20  
  Purchase #5 $191.49   11.630%   $213.7603   $213.76   $213.75   $213.80  
  Purchase #6 $236.90   5.675%   $250.3441   $250.34   $250.35   $250.30  
  Purchase #7 $9.84   6.121%   $10.4423   $10.44   $10.45   $10.40  
  7 purchase totals = $897.09       $983.7714   $983.77   $983.80   $983.70