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 $105.49   11.233%   $117.3397   $117.34   $117.35   $117.30  
  Purchase #2 $120.53   13.129%   $136.3544   $136.35   $136.35   $136.40  
  Purchase #3 $86.77   9.758%   $95.237   $95.24   $95.25   $95.20  
  Purchase #4 $214.41   13.125%   $242.5513   $242.55   $242.55   $242.60  
  Purchase #5 $85.87   8.300%   $92.9972   $93.00   $93.00   $93.00  
  Purchase #6 $149.45   12.365%   $167.9295   $167.93   $167.95   $167.90  
  Purchase #7 $90.68   6.597%   $96.6622   $96.66   $96.65   $96.70  
  7 purchase totals = $853.20       $949.0713   $949.07   $949.10   $949.10