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 $194.46   11.441%   $216.7082   $216.71   $216.70   $216.70  
  Purchase #2 $244.77   9.485%   $267.9864   $267.99   $268.00   $268.00  
  Purchase #3 $82.85   13.371%   $93.9279   $93.93   $93.95   $93.90  
  Purchase #4 $142.76   12.776%   $160.999   $161.00   $161.00   $161.00  
  Purchase #5 $71.85   12.808%   $81.0525   $81.05   $81.05   $81.10  
  Purchase #6 $15.37   12.345%   $17.2674   $17.27   $17.25   $17.30  
  Purchase #7 $227.46   13.432%   $258.0124   $258.01   $258.00   $258.00  
  7 purchase totals = $979.52       $1,095.9538   $1,095.96   $1,095.95   $1,096.00