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 $201.68   10.348%   $222.5498   $222.55   $222.55   $222.50  
  Purchase #2 $209.96   12.856%   $236.9525   $236.95   $236.95   $237.00  
  Purchase #3 $22.79   6.639%   $24.303   $24.30   $24.30   $24.30  
  Purchase #4 $96.73   4.608%   $101.1873   $101.19   $101.20   $101.20  
  Purchase #5 $241.98   4.617%   $253.1522   $253.15   $253.15   $253.20  
  Purchase #6 $207.41   8.861%   $225.7886   $225.79   $225.80   $225.80  
  Purchase #7 $158.31   6.509%   $168.6144   $168.61   $168.60   $168.60  
  7 purchase totals = $1,138.86       $1,232.5478   $1,232.54   $1,232.55   $1,232.60