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 $53.51   9.142%   $58.4019   $58.40   $58.40   $58.40  
  Purchase #2 $171.58   11.738%   $191.7201   $191.72   $191.70   $191.70  
  Purchase #3 $16.69   10.547%   $18.4503   $18.45   $18.45   $18.50  
  Purchase #4 $219.47   10.449%   $242.4024   $242.40   $242.40   $242.40  
  Purchase #5 $41.48   6.700%   $44.2592   $44.26   $44.25   $44.30  
  Purchase #6 $245.94   6.357%   $261.5744   $261.57   $261.55   $261.60  
  Purchase #7 $129.26   12.560%   $145.4951   $145.50   $145.50   $145.50  
  7 purchase totals = $877.93       $962.3034   $962.30   $962.25   $962.40