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 $218.48   6.765%   $233.2602   $233.26   $233.25   $233.30  
  Purchase #2 $86.86   6.742%   $92.7161   $92.72   $92.70   $92.70  
  Purchase #3 $38.74   5.653%   $40.93   $40.93   $40.95   $40.90  
  Purchase #4 $155.51   12.509%   $174.9627   $174.96   $174.95   $175.00  
  Purchase #5 $199.49   4.460%   $208.3873   $208.39   $208.40   $208.40  
  Purchase #6 $107.97   6.542%   $115.0334   $115.03   $115.05   $115.00  
  Purchase #7 $156.86   5.637%   $165.7022   $165.70   $165.70   $165.70  
  7 purchase totals = $963.91       $1,030.9919   $1,030.99   $1,031.00   $1,031.00