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 $54.37   8.572%   $59.0306   $59.03   $59.05   $59.00  
  Purchase #2 $112.39   9.868%   $123.4806   $123.48   $123.50   $123.50  
  Purchase #3 $241.25   13.241%   $273.1939   $273.19   $273.20   $273.20  
  Purchase #4 $220.91   11.649%   $246.6438   $246.64   $246.65   $246.60  
  Purchase #5 $245.68   5.611%   $259.4651   $259.47   $259.45   $259.50  
  Purchase #6 $60.78   3.634%   $62.9887   $62.99   $63.00   $63.00  
  Purchase #7 $164.96   11.520%   $183.9634   $183.96   $183.95   $184.00  
  7 purchase totals = $1,100.34       $1,208.7661   $1,208.76   $1,208.80   $1,208.80