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 $193.81   6.771%   $206.9329   $206.93   $206.95   $206.90  
  Purchase #2 $227.83   4.860%   $238.9025   $238.90   $238.90   $238.90  
  Purchase #3 $119.47   4.672%   $125.0516   $125.05   $125.05   $125.10  
  Purchase #4 $53.39   6.537%   $56.8801   $56.88   $56.90   $56.90  
  Purchase #5 $236.56   13.195%   $267.7741   $267.77   $267.75   $267.80  
  Purchase #6 $114.99   11.186%   $127.8528   $127.85   $127.85   $127.90  
  Purchase #7 $24.59   8.873%   $26.7719   $26.77   $26.75   $26.80  
  7 purchase totals = $970.64       $1,050.1659   $1,050.15   $1,050.15   $1,050.30