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 $56.76   3.267%   $58.6143   $58.61   $58.60   $58.60  
  Purchase #2 $176.51   8.685%   $191.8399   $191.84   $191.85   $191.80  
  Purchase #3 $177.54   11.851%   $198.5803   $198.58   $198.60   $198.60  
  Purchase #4 $84.56   10.702%   $93.6096   $93.61   $93.60   $93.60  
  Purchase #5 $216.63   8.787%   $235.6653   $235.67   $235.65   $235.70  
  Purchase #6 $146.74   5.723%   $155.1379   $155.14   $155.15   $155.10  
  Purchase #7 $91.53   12.320%   $102.8065   $102.81   $102.80   $102.80  
  7 purchase totals = $950.27       $1,036.2538   $1,036.26   $1,036.25   $1,036.20