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 $206.33   11.764%   $230.6027   $230.60   $230.60   $230.60  
  Purchase #2 $49.64   8.147%   $53.6842   $53.68   $53.70   $53.70  
  Purchase #3 $60.73   13.822%   $69.1241   $69.12   $69.10   $69.10  
  Purchase #4 $114.71   7.221%   $122.9932   $122.99   $123.00   $123.00  
  Purchase #5 $240.94   7.520%   $259.0587   $259.06   $259.05   $259.10  
  Purchase #6 $68.80   8.361%   $74.5524   $74.55   $74.55   $74.60  
  Purchase #7 $74.42   10.609%   $82.3152   $82.32   $82.30   $82.30  
  7 purchase totals = $815.57       $892.3305   $892.32   $892.30   $892.40