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 $176.41   13.177%   $199.6555   $199.66   $199.65   $199.70  
  Purchase #2 $91.77   3.539%   $95.0177   $95.02   $95.00   $95.00  
  Purchase #3 $122.71   4.733%   $128.5179   $128.52   $128.50   $128.50  
  Purchase #4 $26.38   3.216%   $27.2284   $27.23   $27.25   $27.20  
  Purchase #5 $142.99   8.704%   $155.4358   $155.44   $155.45   $155.40  
  Purchase #6 $70.32   5.675%   $74.3107   $74.31   $74.30   $74.30  
  Purchase #7 $53.57   5.339%   $56.4301   $56.43   $56.45   $56.40  
  7 purchase totals = $684.15       $736.5961   $736.61   $736.60   $736.50