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 $212.30   13.848%   $241.6993   $241.70   $241.70   $241.70  
  Purchase #2 $133.88   5.208%   $140.8525   $140.85   $140.85   $140.90  
  Purchase #3 $52.68   12.594%   $59.3145   $59.31   $59.30   $59.30  
  Purchase #4 $243.95   10.461%   $269.4696   $269.47   $269.45   $269.50  
  Purchase #5 $105.97   13.862%   $120.6596   $120.66   $120.65   $120.70  
  Purchase #6 $240.42   8.734%   $261.4183   $261.42   $261.40   $261.40  
  Purchase #7 $164.45   6.302%   $174.8136   $174.81   $174.80   $174.80  
  7 purchase totals = $1,153.65       $1,268.2274   $1,268.22   $1,268.15   $1,268.30