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 $61.83   5.596%   $65.29   $65.29   $65.30   $65.30  
  Purchase #2 $114.71   8.472%   $124.4282   $124.43   $124.45   $124.40  
  Purchase #3 $48.69   6.277%   $51.7463   $51.75   $51.75   $51.70  
  Purchase #4 $248.91   10.329%   $274.6199   $274.62   $274.60   $274.60  
  Purchase #5 $236.26   10.268%   $260.5192   $260.52   $260.50   $260.50  
  Purchase #6 $139.95   5.725%   $147.9621   $147.96   $147.95   $148.00  
  Purchase #7 $196.33   8.855%   $213.715   $213.72   $213.70   $213.70  
  7 purchase totals = $1,046.68       $1,138.2807   $1,138.29   $1,138.25   $1,138.20