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 $228.38   5.765%   $241.5461   $241.55   $241.55   $241.50  
  Purchase #2 $149.70   3.502%   $154.9425   $154.94   $154.95   $154.90  
  Purchase #3 $164.76   4.656%   $172.4312   $172.43   $172.45   $172.40  
  Purchase #4 $110.60   4.747%   $115.8502   $115.85   $115.85   $115.90  
  Purchase #5 $193.51   11.520%   $215.8024   $215.80   $215.80   $215.80  
  Purchase #6 $140.74   4.611%   $147.2295   $147.23   $147.25   $147.20  
  Purchase #7 $216.63   4.611%   $226.6188   $226.62   $226.60   $226.60  
  7 purchase totals = $1,204.32       $1,274.4207   $1,274.42   $1,274.45   $1,274.30