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 $236.53   13.668%   $268.8589   $268.86   $268.85   $268.90  
  Purchase #2 $112.45   5.462%   $118.592   $118.59   $118.60   $118.60  
  Purchase #3 $163.89   7.378%   $175.9818   $175.98   $176.00   $176.00  
  Purchase #4 $100.43   7.228%   $107.6891   $107.69   $107.70   $107.70  
  Purchase #5 $183.75   3.459%   $190.1059   $190.11   $190.10   $190.10  
  Purchase #6 $200.41   3.505%   $207.4344   $207.43   $207.45   $207.40  
  Purchase #7 $63.93   5.455%   $67.4174   $67.42   $67.40   $67.40  
  7 purchase totals = $1,061.39       $1,136.0795   $1,136.08   $1,136.10   $1,136.10