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 $249.63   7.770%   $269.0263   $269.03   $269.05   $269.00  
  Purchase #2 $80.88   3.653%   $83.8345   $83.83   $83.85   $83.80  
  Purchase #3 $81.45   8.764%   $88.5883   $88.59   $88.60   $88.60  
  Purchase #4 $112.69   3.262%   $116.3659   $116.37   $116.35   $116.40  
  Purchase #5 $164.81   3.241%   $170.1515   $170.15   $170.15   $170.20  
  Purchase #6 $212.53   11.149%   $236.225   $236.23   $236.25   $236.20  
  Purchase #7 $57.87   12.582%   $65.1512   $65.15   $65.15   $65.20  
  7 purchase totals = $959.86       $1,029.3427   $1,029.35   $1,029.40   $1,029.40