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 $237.51   9.848%   $260.9   $260.90   $260.90   $260.90  
  Purchase #2 $226.55   9.774%   $248.693   $248.69   $248.70   $248.70  
  Purchase #3 $124.87   9.644%   $136.9125   $136.91   $136.90   $136.90  
  Purchase #4 $171.27   8.608%   $186.0129   $186.01   $186.00   $186.00  
  Purchase #5 $207.91   8.118%   $224.7881   $224.79   $224.80   $224.80  
  Purchase #6 $202.29   7.237%   $216.9297   $216.93   $216.95   $216.90  
  Purchase #7 $194.67   7.185%   $208.657   $208.66   $208.65   $208.70  
  7 purchase totals = $1,365.07       $1,482.8932   $1,482.89   $1,482.90   $1,482.90