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 $229.63   13.814%   $261.3511   $261.35   $261.35   $261.40  
  Purchase #2 $174.78   7.349%   $187.6246   $187.62   $187.60   $187.60  
  Purchase #3 $57.75   8.398%   $62.5998   $62.60   $62.60   $62.60  
  Purchase #4 $86.49   13.489%   $98.1566   $98.16   $98.15   $98.20  
  Purchase #5 $165.42   7.861%   $178.4237   $178.42   $178.40   $178.40  
  Purchase #6 $201.37   5.570%   $212.5863   $212.59   $212.60   $212.60  
  Purchase #7 $70.91   9.783%   $77.8471   $77.85   $77.85   $77.80  
  7 purchase totals = $986.35       $1,078.5892   $1,078.59   $1,078.55   $1,078.60