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 $23.34   12.586%   $26.2776   $26.28   $26.30   $26.30  
  Purchase #2 $159.83   7.122%   $171.2131   $171.21   $171.20   $171.20  
  Purchase #3 $68.38   11.450%   $76.2095   $76.21   $76.20   $76.20  
  Purchase #4 $226.73   9.529%   $248.3351   $248.34   $248.35   $248.30  
  Purchase #5 $190.36   9.265%   $207.9969   $208.00   $208.00   $208.00  
  Purchase #6 $232.59   8.352%   $252.0159   $252.02   $252.00   $252.00  
  Purchase #7 $94.46   5.546%   $99.6988   $99.70   $99.70   $99.70  
  7 purchase totals = $995.69       $1,081.7469   $1,081.76   $1,081.75   $1,081.70