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 $105.60   13.311%   $119.6564   $119.66   $119.65   $119.70  
  Purchase #2 $172.76   12.147%   $193.7452   $193.75   $193.75   $193.70  
  Purchase #3 $90.42   8.819%   $98.3941   $98.39   $98.40   $98.40  
  Purchase #4 $136.79   10.674%   $151.391   $151.39   $151.40   $151.40  
  Purchase #5 $170.81   6.324%   $181.612   $181.61   $181.60   $181.60  
  Purchase #6 $167.52   12.786%   $188.9391   $188.94   $188.95   $188.90  
  Purchase #7 $246.79   11.455%   $275.0598   $275.06   $275.05   $275.10  
  7 purchase totals = $1,090.69       $1,208.7976   $1,208.80   $1,208.80   $1,208.80