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 $186.33   13.574%   $211.6224   $211.62   $211.60   $211.60  
  Purchase #2 $236.97   7.776%   $255.3968   $255.40   $255.40   $255.40  
  Purchase #3 $8.59   8.353%   $9.3075   $9.31   $9.30   $9.30  
  Purchase #4 $123.85   3.109%   $127.7005   $127.70   $127.70   $127.70  
  Purchase #5 $240.81   3.514%   $249.2721   $249.27   $249.25   $249.30  
  Purchase #6 $195.59   5.825%   $206.9831   $206.98   $207.00   $207.00  
  Purchase #7 $99.95   13.633%   $113.5762   $113.58   $113.60   $113.60  
  7 purchase totals = $1,092.09       $1,173.8586   $1,173.86   $1,173.85   $1,173.90