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 $235.41   11.522%   $262.5339   $262.53   $262.55   $262.50  
  Purchase #2 $6.30   5.821%   $6.6667   $6.67   $6.65   $6.70  
  Purchase #3 $207.94   9.553%   $227.8045   $227.80   $227.80   $227.80  
  Purchase #4 $67.42   9.630%   $73.9125   $73.91   $73.90   $73.90  
  Purchase #5 $232.88   10.828%   $258.0962   $258.10   $258.10   $258.10  
  Purchase #6 $193.96   12.215%   $217.6522   $217.65   $217.65   $217.70  
  Purchase #7 $10.33   9.366%   $11.2975   $11.30   $11.30   $11.30  
  7 purchase totals = $954.24       $1,057.9635   $1,057.96   $1,057.95   $1,058.00