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 $206.58   12.596%   $232.6008   $232.60   $232.60   $232.60  
  Purchase #2 $19.99   13.355%   $22.6597   $22.66   $22.65   $22.70  
  Purchase #3 $61.77   3.583%   $63.9832   $63.98   $64.00   $64.00  
  Purchase #4 $230.74   10.791%   $255.6392   $255.64   $255.65   $255.60  
  Purchase #5 $242.77   12.456%   $273.0094   $273.01   $273.00   $273.00  
  Purchase #6 $59.87   7.322%   $64.2537   $64.25   $64.25   $64.30  
  Purchase #7 $6.32   10.366%   $6.9751   $6.98   $7.00   $7.00  
  7 purchase totals = $828.04       $919.1211   $919.12   $919.15   $919.20