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 $160.91   11.102%   $178.7742   $178.77   $178.75   $178.80  
  Purchase #2 $208.54   8.292%   $225.8321   $225.83   $225.85   $225.80  
  Purchase #3 $50.30   3.838%   $52.2305   $52.23   $52.25   $52.20  
  Purchase #4 $27.50   7.853%   $29.6596   $29.66   $29.65   $29.70  
  Purchase #5 $89.40   4.536%   $93.4552   $93.46   $93.45   $93.50  
  Purchase #6 $180.61   9.329%   $197.4591   $197.46   $197.45   $197.50  
  Purchase #7 $230.25   7.839%   $248.2993   $248.30   $248.30   $248.30  
  7 purchase totals = $947.51       $1,025.7100   $1,025.71   $1,025.70   $1,025.80