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 $59.50   6.129%   $63.1468   $63.15   $63.15   $63.10  
  Purchase #2 $33.27   11.750%   $37.1792   $37.18   $37.20   $37.20  
  Purchase #3 $231.37   3.326%   $239.0654   $239.07   $239.05   $239.10  
  Purchase #4 $237.62   8.562%   $257.965   $257.97   $257.95   $258.00  
  Purchase #5 $164.88   12.799%   $185.983   $185.98   $186.00   $186.00  
  Purchase #6 $225.36   7.493%   $242.2462   $242.25   $242.25   $242.20  
  Purchase #7 $171.90   3.206%   $177.4111   $177.41   $177.40   $177.40  
  7 purchase totals = $1,123.90       $1,202.9967   $1,203.01   $1,203.00   $1,203.00