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 $85.69   13.647%   $97.3841   $97.38   $97.40   $97.40  
  Purchase #2 $233.96   12.538%   $263.2939   $263.29   $263.30   $263.30  
  Purchase #3 $42.94   8.757%   $46.7003   $46.70   $46.70   $46.70  
  Purchase #4 $203.93   8.650%   $221.5699   $221.57   $221.55   $221.60  
  Purchase #5 $165.28   12.563%   $186.0441   $186.04   $186.05   $186.00  
  Purchase #6 $54.32   4.707%   $56.8768   $56.88   $56.90   $56.90  
  Purchase #7 $127.88   4.517%   $133.6563   $133.66   $133.65   $133.70  
  7 purchase totals = $914.00       $1,005.5254   $1,005.52   $1,005.55   $1,005.60