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 $193.54   6.292%   $205.7175   $205.72   $205.70   $205.70  
  Purchase #2 $216.36   13.387%   $245.3241   $245.32   $245.30   $245.30  
  Purchase #3 $248.60   6.845%   $265.6167   $265.62   $265.60   $265.60  
  Purchase #4 $134.40   12.742%   $151.5252   $151.53   $151.55   $151.50  
  Purchase #5 $248.80   10.495%   $274.9116   $274.91   $274.90   $274.90  
  Purchase #6 $167.90   5.489%   $177.116   $177.12   $177.10   $177.10  
  Purchase #7 $141.31   3.376%   $146.0806   $146.08   $146.10   $146.10  
  7 purchase totals = $1,350.91       $1,466.2917   $1,466.30   $1,466.25   $1,466.20