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 $236.31   6.813%   $252.4098   $252.41   $252.40   $252.40  
  Purchase #2 $54.29   3.590%   $56.239   $56.24   $56.25   $56.20  
  Purchase #3 $51.69   12.315%   $58.0556   $58.06   $58.05   $58.10  
  Purchase #4 $191.26   7.167%   $204.9676   $204.97   $204.95   $205.00  
  Purchase #5 $180.66   10.493%   $199.6167   $199.62   $199.60   $199.60  
  Purchase #6 $189.41   6.620%   $201.9489   $201.95   $201.95   $201.90  
  Purchase #7 $88.60   9.109%   $96.6706   $96.67   $96.65   $96.70  
  7 purchase totals = $992.22       $1,069.9082   $1,069.92   $1,069.85   $1,069.90