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 $196.72   13.199%   $222.6851   $222.69   $222.70   $222.70  
  Purchase #2 $248.61   10.691%   $275.1889   $275.19   $275.20   $275.20  
  Purchase #3 $209.62   5.417%   $220.9751   $220.98   $221.00   $221.00  
  Purchase #4 $106.77   7.261%   $114.5226   $114.52   $114.50   $114.50  
  Purchase #5 $110.83   5.102%   $116.4845   $116.48   $116.50   $116.50  
  Purchase #6 $235.99   5.295%   $248.4857   $248.49   $248.50   $248.50  
  Purchase #7 $59.66   13.331%   $67.6133   $67.61   $67.60   $67.60  
  7 purchase totals = $1,168.20       $1,265.9552   $1,265.96   $1,266.00   $1,266.00