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 $183.25   13.623%   $208.2141   $208.21   $208.20   $208.20  
  Purchase #2 $246.66   3.230%   $254.6271   $254.63   $254.65   $254.60  
  Purchase #3 $118.35   4.815%   $124.0486   $124.05   $124.05   $124.00  
  Purchase #4 $119.65   12.442%   $134.5369   $134.54   $134.55   $134.50  
  Purchase #5 $143.99   11.858%   $161.0643   $161.06   $161.05   $161.10  
  Purchase #6 $8.52   12.820%   $9.6123   $9.61   $9.60   $9.60  
  Purchase #7 $125.49   11.594%   $140.0393   $140.04   $140.05   $140.00  
  7 purchase totals = $945.91       $1,032.1426   $1,032.14   $1,032.15   $1,032.00