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 $59.61   6.353%   $63.397   $63.40   $63.40   $63.40  
  Purchase #2 $163.35   11.634%   $182.3541   $182.35   $182.35   $182.40  
  Purchase #3 $225.26   6.399%   $239.6744   $239.67   $239.65   $239.70  
  Purchase #4 $24.68   12.508%   $27.767   $27.77   $27.75   $27.80  
  Purchase #5 $210.48   5.708%   $222.4942   $222.49   $222.50   $222.50  
  Purchase #6 $202.81   11.658%   $226.4536   $226.45   $226.45   $226.50  
  Purchase #7 $154.93   13.263%   $175.4784   $175.48   $175.50   $175.50  
  7 purchase totals = $1,041.12       $1,137.6187   $1,137.61   $1,137.60   $1,137.80