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 $225.43   7.293%   $241.8706   $241.87   $241.85   $241.90  
  Purchase #2 $18.76   5.532%   $19.7978   $19.80   $19.80   $19.80  
  Purchase #3 $232.88   5.308%   $245.2413   $245.24   $245.25   $245.20  
  Purchase #4 $180.95   6.864%   $193.3704   $193.37   $193.35   $193.40  
  Purchase #5 $113.91   11.869%   $127.43   $127.43   $127.45   $127.40  
  Purchase #6 $115.66   7.859%   $124.7497   $124.75   $124.75   $124.70  
  Purchase #7 $179.44   10.817%   $198.85   $198.85   $198.85   $198.90  
  7 purchase totals = $1,067.03       $1,151.3098   $1,151.31   $1,151.30   $1,151.30