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 $42.72   8.278%   $46.2564   $46.26   $46.25   $46.30  
  Purchase #2 $122.29   5.337%   $128.8166   $128.82   $128.80   $128.80  
  Purchase #3 $228.31   8.436%   $247.5702   $247.57   $247.55   $247.60  
  Purchase #4 $46.27   3.151%   $47.728   $47.73   $47.75   $47.70  
  Purchase #5 $79.47   3.200%   $82.013   $82.01   $82.00   $82.00  
  Purchase #6 $107.25   4.665%   $112.2532   $112.25   $112.25   $112.30  
  Purchase #7 $242.71   9.653%   $266.1388   $266.14   $266.15   $266.10  
  7 purchase totals = $869.02       $930.7762   $930.78   $930.75   $930.80