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 $165.77   12.726%   $186.8659   $186.87   $186.85   $186.90  
  Purchase #2 $244.97   5.621%   $258.7398   $258.74   $258.75   $258.70  
  Purchase #3 $33.71   11.594%   $37.6183   $37.62   $37.60   $37.60  
  Purchase #4 $192.77   8.212%   $208.6003   $208.60   $208.60   $208.60  
  Purchase #5 $175.64   13.108%   $198.6629   $198.66   $198.65   $198.70  
  Purchase #6 $58.62   6.629%   $62.5059   $62.51   $62.50   $62.50  
  Purchase #7 $103.44   3.321%   $106.8752   $106.88   $106.90   $106.90  
  7 purchase totals = $974.92       $1,059.8683   $1,059.88   $1,059.85   $1,059.90