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 $57.46   8.776%   $62.5027   $62.50   $62.50   $62.50  
  Purchase #2 $14.66   9.600%   $16.0674   $16.07   $16.05   $16.10  
  Purchase #3 $109.43   12.690%   $123.3167   $123.32   $123.30   $123.30  
  Purchase #4 $200.53   6.787%   $214.14   $214.14   $214.15   $214.10  
  Purchase #5 $24.33   8.337%   $26.3584   $26.36   $26.35   $26.40  
  Purchase #6 $233.52   3.627%   $241.9898   $241.99   $242.00   $242.00  
  Purchase #7 $236.73   12.182%   $265.5684   $265.57   $265.55   $265.60  
  7 purchase totals = $876.66       $949.9434   $949.95   $949.90   $950.00