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 $243.95   9.546%   $267.2375   $267.24   $267.25   $267.20  
  Purchase #2 $123.34   12.713%   $139.0202   $139.02   $139.00   $139.00  
  Purchase #3 $92.31   3.366%   $95.4172   $95.42   $95.40   $95.40  
  Purchase #4 $114.99   4.282%   $119.9139   $119.91   $119.90   $119.90  
  Purchase #5 $26.39   5.475%   $27.8349   $27.83   $27.85   $27.80  
  Purchase #6 $228.33   7.199%   $244.7675   $244.77   $244.75   $244.80  
  Purchase #7 $119.39   3.545%   $123.6224   $123.62   $123.60   $123.60  
  7 purchase totals = $948.70       $1,017.8136   $1,017.81   $1,017.75   $1,017.70