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 $171.69   12.347%   $192.8886   $192.89   $192.90   $192.90  
  Purchase #2 $248.32   8.380%   $269.1292   $269.13   $269.15   $269.10  
  Purchase #3 $67.47   10.739%   $74.7156   $74.72   $74.70   $74.70  
  Purchase #4 $59.95   7.286%   $64.318   $64.32   $64.30   $64.30  
  Purchase #5 $103.34   12.529%   $116.2875   $116.29   $116.30   $116.30  
  Purchase #6 $63.40   4.440%   $66.215   $66.22   $66.20   $66.20  
  Purchase #7 $211.64   7.569%   $227.659   $227.66   $227.65   $227.70  
  7 purchase totals = $925.81       $1,011.2129   $1,011.23   $1,011.20   $1,011.20