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 $85.83   10.207%   $94.5907   $94.59   $94.60   $94.60  
  Purchase #2 $175.95   7.772%   $189.6248   $189.62   $189.60   $189.60  
  Purchase #3 $13.99   10.756%   $15.4948   $15.49   $15.50   $15.50  
  Purchase #4 $191.55   8.722%   $208.257   $208.26   $208.25   $208.30  
  Purchase #5 $26.81   10.866%   $29.7232   $29.72   $29.70   $29.70  
  Purchase #6 $150.54   12.717%   $169.6842   $169.68   $169.70   $169.70  
  Purchase #7 $213.72   5.226%   $224.889   $224.89   $224.90   $224.90  
  7 purchase totals = $858.39       $932.2637   $932.25   $932.25   $932.30