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 $58.58   7.372%   $62.8985   $62.90   $62.90   $62.90  
  Purchase #2 $187.38   10.578%   $207.2011   $207.20   $207.20   $207.20  
  Purchase #3 $114.82   10.151%   $126.4754   $126.48   $126.50   $126.50  
  Purchase #4 $196.61   12.744%   $221.666   $221.67   $221.65   $221.70  
  Purchase #5 $87.36   3.256%   $90.2044   $90.20   $90.20   $90.20  
  Purchase #6 $117.90   4.247%   $122.9072   $122.91   $122.90   $122.90  
  Purchase #7 $61.93   7.112%   $66.3345   $66.33   $66.35   $66.30  
  7 purchase totals = $824.58       $897.6871   $897.69   $897.70   $897.70