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 $239.35   12.601%   $269.5105   $269.51   $269.50   $269.50  
  Purchase #2 $101.42   7.791%   $109.3216   $109.32   $109.30   $109.30  
  Purchase #3 $106.56   7.271%   $114.308   $114.31   $114.30   $114.30  
  Purchase #4 $170.68   6.446%   $181.682   $181.68   $181.70   $181.70  
  Purchase #5 $206.35   9.449%   $225.848   $225.85   $225.85   $225.80  
  Purchase #6 $104.88   8.574%   $113.8724   $113.87   $113.85   $113.90  
  Purchase #7 $73.93   4.349%   $77.1452   $77.15   $77.15   $77.10  
  7 purchase totals = $1,003.17       $1,091.6877   $1,091.69   $1,091.65   $1,091.60