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 $52.68   9.327%   $57.5935   $57.59   $57.60   $57.60  
  Purchase #2 $80.97   7.267%   $86.8541   $86.85   $86.85   $86.90  
  Purchase #3 $99.59   4.290%   $103.8624   $103.86   $103.85   $103.90  
  Purchase #4 $46.93   10.591%   $51.9004   $51.90   $51.90   $51.90  
  Purchase #5 $195.63   6.660%   $208.659   $208.66   $208.65   $208.70  
  Purchase #6 $108.41   10.832%   $120.153   $120.15   $120.15   $120.20  
  Purchase #7 $42.88   5.366%   $45.1809   $45.18   $45.20   $45.20  
  7 purchase totals = $627.09       $674.2033   $674.19   $674.20   $674.40