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 $32.26   11.566%   $35.9912   $35.99   $36.00   $36.00  
  Purchase #2 $240.43   3.471%   $248.7753   $248.78   $248.80   $248.80  
  Purchase #3 $109.78   12.704%   $123.7265   $123.73   $123.75   $123.70  
  Purchase #4 $78.48   11.724%   $87.681   $87.68   $87.70   $87.70  
  Purchase #5 $23.82   13.186%   $26.9609   $26.96   $26.95   $27.00  
  Purchase #6 $175.47   12.650%   $197.667   $197.67   $197.65   $197.70  
  Purchase #7 $164.32   12.749%   $185.2692   $185.27   $185.25   $185.30  
  7 purchase totals = $824.56       $906.0711   $906.08   $906.10   $906.20