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 $175.52   6.185%   $186.3759   $186.38   $186.40   $186.40  
  Purchase #2 $250.64   6.515%   $266.9692   $266.97   $266.95   $267.00  
  Purchase #3 $90.74   7.669%   $97.6989   $97.70   $97.70   $97.70  
  Purchase #4 $225.91   6.447%   $240.4744   $240.47   $240.45   $240.50  
  Purchase #5 $245.68   5.783%   $259.8877   $259.89   $259.90   $259.90  
  Purchase #6 $61.38   12.439%   $69.0151   $69.02   $69.00   $69.00  
  Purchase #7 $133.92   13.671%   $152.2282   $152.23   $152.25   $152.20  
  7 purchase totals = $1,183.79       $1,272.6494   $1,272.66   $1,272.65   $1,272.70