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 $192.68   11.137%   $214.1388   $214.14   $214.15   $214.10  
  Purchase #2 $179.65   12.215%   $201.5942   $201.59   $201.60   $201.60  
  Purchase #3 $52.70   11.333%   $58.6725   $58.67   $58.65   $58.70  
  Purchase #4 $230.80   7.679%   $248.5231   $248.52   $248.50   $248.50  
  Purchase #5 $237.71   10.366%   $262.351   $262.35   $262.35   $262.40  
  Purchase #6 $134.60   9.141%   $146.9038   $146.90   $146.90   $146.90  
  Purchase #7 $108.91   13.171%   $123.2545   $123.25   $123.25   $123.30  
  7 purchase totals = $1,137.05       $1,255.4379   $1,255.42   $1,255.40   $1,255.50