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 $229.82   5.844%   $243.2507   $243.25   $243.25   $243.30  
  Purchase #2 $146.86   11.570%   $163.8517   $163.85   $163.85   $163.90  
  Purchase #3 $148.38   6.482%   $157.998   $158.00   $158.00   $158.00  
  Purchase #4 $225.44   10.493%   $249.0954   $249.10   $249.10   $249.10  
  Purchase #5 $248.80   9.561%   $272.5878   $272.59   $272.60   $272.60  
  Purchase #6 $62.33   12.284%   $69.9866   $69.99   $70.00   $70.00  
  Purchase #7 $186.60   7.768%   $201.0951   $201.10   $201.10   $201.10  
  7 purchase totals = $1,248.23       $1,357.8653   $1,357.88   $1,357.90   $1,358.00