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 $63.76   5.111%   $67.0188   $67.02   $67.00   $67.00  
  Purchase #2 $90.66   7.482%   $97.4432   $97.44   $97.45   $97.40  
  Purchase #3 $117.80   13.656%   $133.8868   $133.89   $133.90   $133.90  
  Purchase #4 $127.85   3.655%   $132.5229   $132.52   $132.50   $132.50  
  Purchase #5 $209.70   8.732%   $228.011   $228.01   $228.00   $228.00  
  Purchase #6 $105.85   8.293%   $114.6281   $114.63   $114.65   $114.60  
  Purchase #7 $214.46   11.655%   $239.4553   $239.46   $239.45   $239.50  
  7 purchase totals = $930.08       $1,012.9661   $1,012.97   $1,012.95   $1,012.90