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 $49.39   4.656%   $51.6896   $51.69   $51.70   $51.70  
  Purchase #2 $134.57   9.612%   $147.5049   $147.50   $147.50   $147.50  
  Purchase #3 $152.90   12.350%   $171.7832   $171.78   $171.80   $171.80  
  Purchase #4 $173.67   13.854%   $197.7302   $197.73   $197.75   $197.70  
  Purchase #5 $242.93   6.725%   $259.267   $259.27   $259.25   $259.30  
  Purchase #6 $177.84   4.552%   $185.9353   $185.94   $185.95   $185.90  
  Purchase #7 $57.53   7.709%   $61.965   $61.97   $61.95   $62.00  
  7 purchase totals = $988.83       $1,075.8752   $1,075.88   $1,075.90   $1,075.90