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 $228.94   4.513%   $239.2721   $239.27   $239.25   $239.30  
  Purchase #2 $123.57   11.301%   $137.5346   $137.53   $137.55   $137.50  
  Purchase #3 $237.42   9.770%   $260.6159   $260.62   $260.60   $260.60  
  Purchase #4 $202.58   3.469%   $209.6075   $209.61   $209.60   $209.60  
  Purchase #5 $77.27   3.143%   $79.6986   $79.70   $79.70   $79.70  
  Purchase #6 $149.77   11.752%   $167.371   $167.37   $167.35   $167.40  
  Purchase #7 $99.97   13.821%   $113.7869   $113.79   $113.80   $113.80  
  7 purchase totals = $1,119.52       $1,207.8866   $1,207.89   $1,207.85   $1,207.90