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 $144.72   12.654%   $163.0329   $163.03   $163.05   $163.00  
  Purchase #2 $127.72   6.628%   $136.1853   $136.19   $136.20   $136.20  
  Purchase #3 $164.30   7.153%   $176.0524   $176.05   $176.05   $176.10  
  Purchase #4 $185.45   10.182%   $204.3325   $204.33   $204.35   $204.30  
  Purchase #5 $24.65   8.590%   $26.7674   $26.77   $26.75   $26.80  
  Purchase #6 $178.29   11.509%   $198.8094   $198.81   $198.80   $198.80  
  Purchase #7 $107.92   7.569%   $116.0885   $116.09   $116.10   $116.10  
  7 purchase totals = $933.05       $1,021.2684   $1,021.27   $1,021.30   $1,021.30