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 $58.25   6.432%   $61.9966   $62.00   $62.00   $62.00  
  Purchase #2 $184.76   12.161%   $207.2287   $207.23   $207.25   $207.20  
  Purchase #3 $215.25   6.582%   $229.4178   $229.42   $229.40   $229.40  
  Purchase #4 $31.42   7.471%   $33.7674   $33.77   $33.75   $33.80  
  Purchase #5 $15.51   13.310%   $17.5744   $17.57   $17.55   $17.60  
  Purchase #6 $47.30   3.719%   $49.0591   $49.06   $49.05   $49.10  
  Purchase #7 $74.38   4.338%   $77.6066   $77.61   $77.60   $77.60  
  7 purchase totals = $626.87       $676.6506   $676.66   $676.60   $676.70