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 $246.86   8.426%   $267.6604   $267.66   $267.65   $267.70  
  Purchase #2 $70.38   8.508%   $76.3679   $76.37   $76.35   $76.40  
  Purchase #3 $154.26   8.704%   $167.6868   $167.69   $167.70   $167.70  
  Purchase #4 $169.68   5.684%   $179.3246   $179.32   $179.30   $179.30  
  Purchase #5 $68.95   7.682%   $74.2467   $74.25   $74.25   $74.20  
  Purchase #6 $111.25   11.427%   $123.9625   $123.96   $123.95   $124.00  
  Purchase #7 $233.72   4.713%   $244.7352   $244.74   $244.75   $244.70  
  7 purchase totals = $1,055.10       $1,133.9841   $1,133.99   $1,133.95   $1,134.00