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 $209.82   9.224%   $229.1738   $229.17   $229.15   $229.20  
  Purchase #2 $61.31   12.354%   $68.8842   $68.88   $68.90   $68.90  
  Purchase #3 $57.27   10.675%   $63.3836   $63.38   $63.40   $63.40  
  Purchase #4 $235.72   6.371%   $250.7377   $250.74   $250.75   $250.70  
  Purchase #5 $166.77   11.661%   $186.217   $186.22   $186.20   $186.20  
  Purchase #6 $115.87   10.470%   $128.0016   $128.00   $128.00   $128.00  
  Purchase #7 $24.83   5.805%   $26.2714   $26.27   $26.25   $26.30  
  7 purchase totals = $871.59       $952.6693   $952.66   $952.65   $952.70