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 $228.25   11.493%   $254.4828   $254.48   $254.50   $254.50  
  Purchase #2 $249.87   5.200%   $262.8632   $262.86   $262.85   $262.90  
  Purchase #3 $153.40   11.116%   $170.4519   $170.45   $170.45   $170.50  
  Purchase #4 $86.73   12.837%   $97.8635   $97.86   $97.85   $97.90  
  Purchase #5 $32.50   6.579%   $34.6382   $34.64   $34.65   $34.60  
  Purchase #6 $26.91   10.834%   $29.8254   $29.83   $29.85   $29.80  
  Purchase #7 $196.47   9.780%   $215.6848   $215.68   $215.70   $215.70  
  7 purchase totals = $974.13       $1,065.8098   $1,065.80   $1,065.85   $1,065.90