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 $173.27   12.508%   $194.9426   $194.94   $194.95   $194.90  
  Purchase #2 $38.58   5.466%   $40.6888   $40.69   $40.70   $40.70  
  Purchase #3 $229.92   13.475%   $260.9017   $260.90   $260.90   $260.90  
  Purchase #4 $110.35   4.851%   $115.7031   $115.70   $115.70   $115.70  
  Purchase #5 $246.30   11.235%   $273.9718   $273.97   $273.95   $274.00  
  Purchase #6 $200.58   12.797%   $226.2482   $226.25   $226.25   $226.20  
  Purchase #7 $92.56   6.218%   $98.3154   $98.32   $98.30   $98.30  
  7 purchase totals = $1,091.56       $1,210.7716   $1,210.77   $1,210.75   $1,210.70