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 $198.41   13.809%   $225.8084   $225.81   $225.80   $225.80  
  Purchase #2 $192.55   3.726%   $199.7244   $199.72   $199.70   $199.70  
  Purchase #3 $64.77   3.322%   $66.9217   $66.92   $66.90   $66.90  
  Purchase #4 $169.30   7.495%   $181.989   $181.99   $182.00   $182.00  
  Purchase #5 $114.55   10.171%   $126.2009   $126.20   $126.20   $126.20  
  Purchase #6 $209.75   6.649%   $223.6963   $223.70   $223.70   $223.70  
  Purchase #7 $76.89   7.555%   $82.699   $82.70   $82.70   $82.70  
  7 purchase totals = $1,026.22       $1,107.0397   $1,107.04   $1,107.00   $1,107.00