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 $88.75   8.249%   $96.071   $96.07   $96.05   $96.10  
  Purchase #2 $62.68   11.214%   $69.7089   $69.71   $69.70   $69.70  
  Purchase #3 $250.96   11.762%   $280.4779   $280.48   $280.50   $280.50  
  Purchase #4 $183.26   4.601%   $191.6918   $191.69   $191.70   $191.70  
  Purchase #5 $222.93   3.241%   $230.1552   $230.16   $230.15   $230.20  
  Purchase #6 $178.62   9.546%   $195.6711   $195.67   $195.65   $195.70  
  Purchase #7 $11.40   5.587%   $12.0369   $12.04   $12.05   $12.00  
  7 purchase totals = $998.60       $1,075.8128   $1,075.82   $1,075.80   $1,075.90