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 $146.26   5.648%   $154.5208   $154.52   $154.50   $154.50  
  Purchase #2 $250.58   4.458%   $261.7509   $261.75   $261.75   $261.80  
  Purchase #3 $186.70   4.804%   $195.6691   $195.67   $195.65   $195.70  
  Purchase #4 $5.74   6.867%   $6.1342   $6.13   $6.15   $6.10  
  Purchase #5 $57.54   5.436%   $60.6679   $60.67   $60.65   $60.70  
  Purchase #6 $154.69   11.432%   $172.3742   $172.37   $172.35   $172.40  
  Purchase #7 $13.55   12.443%   $15.236   $15.24   $15.25   $15.20  
  7 purchase totals = $815.06       $866.3531   $866.35   $866.30   $866.40