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 $213.43   8.709%   $232.0176   $232.02   $232.00   $232.00  
  Purchase #2 $28.79   3.354%   $29.7556   $29.76   $29.75   $29.80  
  Purchase #3 $193.59   10.497%   $213.9111   $213.91   $213.90   $213.90  
  Purchase #4 $109.89   10.365%   $121.2801   $121.28   $121.30   $121.30  
  Purchase #5 $250.82   9.636%   $274.989   $274.99   $275.00   $275.00  
  Purchase #6 $120.34   5.850%   $127.3799   $127.38   $127.40   $127.40  
  Purchase #7 $234.82   5.779%   $248.3902   $248.39   $248.40   $248.40  
  7 purchase totals = $1,151.68       $1,247.7235   $1,247.73   $1,247.75   $1,247.80