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 $113.59   8.835%   $123.6257   $123.63   $123.65   $123.60  
  Purchase #2 $75.29   10.557%   $83.2384   $83.24   $83.25   $83.20  
  Purchase #3 $90.75   13.255%   $102.7789   $102.78   $102.80   $102.80  
  Purchase #4 $225.30   4.809%   $236.1347   $236.13   $236.15   $236.10  
  Purchase #5 $95.45   3.589%   $98.8757   $98.88   $98.90   $98.90  
  Purchase #6 $231.97   7.115%   $248.4747   $248.47   $248.45   $248.50  
  Purchase #7 $164.26   7.558%   $176.6748   $176.67   $176.65   $176.70  
  7 purchase totals = $996.61       $1,069.8029   $1,069.80   $1,069.85   $1,069.80