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 $232.56   13.309%   $263.5114   $263.51   $263.50   $263.50  
  Purchase #2 $158.45   3.473%   $163.953   $163.95   $163.95   $164.00  
  Purchase #3 $176.88   7.858%   $190.7792   $190.78   $190.80   $190.80  
  Purchase #4 $62.96   11.598%   $70.2621   $70.26   $70.25   $70.30  
  Purchase #5 $95.41   9.728%   $104.6915   $104.69   $104.70   $104.70  
  Purchase #6 $151.42   4.433%   $158.1324   $158.13   $158.15   $158.10  
  Purchase #7 $42.26   4.191%   $44.0311   $44.03   $44.05   $44.00  
  7 purchase totals = $919.94       $995.3607   $995.35   $995.40   $995.40