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 $111.30   7.535%   $119.6865   $119.69   $119.70   $119.70  
  Purchase #2 $20.76   9.709%   $22.7756   $22.78   $22.80   $22.80  
  Purchase #3 $22.26   12.197%   $24.9751   $24.98   $25.00   $25.00  
  Purchase #4 $38.54   12.462%   $43.3429   $43.34   $43.35   $43.30  
  Purchase #5 $52.66   7.613%   $56.669   $56.67   $56.65   $56.70  
  Purchase #6 $235.37   5.732%   $248.8614   $248.86   $248.85   $248.90  
  Purchase #7 $233.32   6.717%   $248.9921   $248.99   $249.00   $249.00  
  7 purchase totals = $714.21       $765.3026   $765.31   $765.35   $765.40