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 $156.81   5.384%   $165.2527   $165.25   $165.25   $165.30  
  Purchase #2 $180.83   10.231%   $199.3307   $199.33   $199.35   $199.30  
  Purchase #3 $179.26   5.622%   $189.338   $189.34   $189.35   $189.30  
  Purchase #4 $216.99   7.263%   $232.75   $232.75   $232.75   $232.80  
  Purchase #5 $88.69   8.402%   $96.1417   $96.14   $96.15   $96.10  
  Purchase #6 $159.62   4.667%   $167.0695   $167.07   $167.05   $167.10  
  Purchase #7 $116.28   9.386%   $127.194   $127.19   $127.20   $127.20  
  7 purchase totals = $1,098.48       $1,177.0766   $1,177.07   $1,177.10   $1,177.10