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 $44.34   11.810%   $49.5766   $49.58   $49.60   $49.60  
  Purchase #2 $155.63   7.871%   $167.8796   $167.88   $167.90   $167.90  
  Purchase #3 $176.96   3.747%   $183.5907   $183.59   $183.60   $183.60  
  Purchase #4 $34.74   6.147%   $36.8755   $36.88   $36.90   $36.90  
  Purchase #5 $164.88   10.198%   $181.6945   $181.69   $181.70   $181.70  
  Purchase #6 $248.77   9.785%   $273.1121   $273.11   $273.10   $273.10  
  Purchase #7 $241.34   7.358%   $259.0978   $259.10   $259.10   $259.10  
  7 purchase totals = $1,066.66       $1,151.8268   $1,151.83   $1,151.90   $1,151.90