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 $223.55   4.332%   $233.2342   $233.23   $233.25   $233.20  
  Purchase #2 $155.68   7.702%   $167.6705   $167.67   $167.65   $167.70  
  Purchase #3 $88.86   7.577%   $95.5929   $95.59   $95.60   $95.60  
  Purchase #4 $236.27   5.216%   $248.5938   $248.59   $248.60   $248.60  
  Purchase #5 $109.40   3.296%   $113.0058   $113.01   $113.00   $113.00  
  Purchase #6 $242.90   12.582%   $273.4617   $273.46   $273.45   $273.50  
  Purchase #7 $163.98   12.115%   $183.8462   $183.85   $183.85   $183.80  
  7 purchase totals = $1,220.64       $1,315.4051   $1,315.40   $1,315.40   $1,315.40