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 $52.92   8.770%   $57.5611   $57.56   $57.55   $57.60  
  Purchase #2 $54.81   11.567%   $61.1499   $61.15   $61.15   $61.10  
  Purchase #3 $230.48   7.474%   $247.7061   $247.71   $247.70   $247.70  
  Purchase #4 $180.95   11.549%   $201.8479   $201.85   $201.85   $201.80  
  Purchase #5 $235.26   7.362%   $252.5798   $252.58   $252.60   $252.60  
  Purchase #6 $114.25   10.558%   $126.3125   $126.31   $126.30   $126.30  
  Purchase #7 $169.38   12.566%   $190.6643   $190.66   $190.65   $190.70  
  7 purchase totals = $1,038.05       $1,137.8216   $1,137.82   $1,137.80   $1,137.80