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 $56.91   3.288%   $58.7812   $58.78   $58.80   $58.80  
  Purchase #2 $94.81   11.469%   $105.6838   $105.68   $105.70   $105.70  
  Purchase #3 $234.72   4.366%   $244.9679   $244.97   $244.95   $245.00  
  Purchase #4 $133.83   6.371%   $142.3563   $142.36   $142.35   $142.40  
  Purchase #5 $179.83   7.844%   $193.9359   $193.94   $193.95   $193.90  
  Purchase #6 $52.57   11.638%   $58.6881   $58.69   $58.70   $58.70  
  Purchase #7 $193.34   11.307%   $215.201   $215.20   $215.20   $215.20  
  7 purchase totals = $946.01       $1,019.6142   $1,019.62   $1,019.65   $1,019.70