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 $245.42   6.723%   $261.9196   $261.92   $261.90   $261.90  
  Purchase #2 $179.37   5.695%   $189.5851   $189.59   $189.60   $189.60  
  Purchase #3 $86.69   11.128%   $96.3369   $96.34   $96.35   $96.30  
  Purchase #4 $214.35   13.359%   $242.985   $242.99   $243.00   $243.00  
  Purchase #5 $62.60   4.813%   $65.6129   $65.61   $65.60   $65.60  
  Purchase #6 $98.30   5.736%   $103.9385   $103.94   $103.95   $103.90  
  Purchase #7 $43.84   8.478%   $47.5568   $47.56   $47.55   $47.60  
  7 purchase totals = $930.57       $1,007.9348   $1,007.95   $1,007.95   $1,007.90