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 $232.59   8.652%   $252.7137   $252.71   $252.70   $252.70  
  Purchase #2 $32.27   6.513%   $34.3717   $34.37   $34.35   $34.40  
  Purchase #3 $85.59   11.449%   $95.3892   $95.39   $95.40   $95.40  
  Purchase #4 $228.96   4.595%   $239.4807   $239.48   $239.50   $239.50  
  Purchase #5 $110.26   3.582%   $114.2095   $114.21   $114.20   $114.20  
  Purchase #6 $241.89   4.517%   $252.8162   $252.82   $252.80   $252.80  
  Purchase #7 $10.51   7.426%   $11.2905   $11.29   $11.30   $11.30  
  7 purchase totals = $942.07       $1,000.2715   $1,000.27   $1,000.25   $1,000.30