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 $111.55   5.111%   $117.2513   $117.25   $117.25   $117.30  
  Purchase #2 $89.70   8.584%   $97.3998   $97.40   $97.40   $97.40  
  Purchase #3 $23.63   13.490%   $26.8177   $26.82   $26.80   $26.80  
  Purchase #4 $153.66   7.504%   $165.1906   $165.19   $165.20   $165.20  
  Purchase #5 $240.95   12.333%   $270.6664   $270.67   $270.65   $270.70  
  Purchase #6 $179.68   6.683%   $191.688   $191.69   $191.70   $191.70  
  Purchase #7 $147.91   12.144%   $165.8722   $165.87   $165.85   $165.90  
  7 purchase totals = $947.08       $1,034.8860   $1,034.89   $1,034.85   $1,035.00