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 $30.82   7.106%   $33.0101   $33.01   $33.00   $33.00  
  Purchase #2 $220.29   7.719%   $237.2942   $237.29   $237.30   $237.30  
  Purchase #3 $168.84   7.660%   $181.7731   $181.77   $181.75   $181.80  
  Purchase #4 $246.83   10.670%   $273.1668   $273.17   $273.15   $273.20  
  Purchase #5 $220.87   13.633%   $250.9812   $250.98   $251.00   $251.00  
  Purchase #6 $163.67   12.414%   $183.988   $183.99   $184.00   $184.00  
  Purchase #7 $79.45   5.193%   $83.5758   $83.58   $83.60   $83.60  
  7 purchase totals = $1,130.77       $1,243.7892   $1,243.79   $1,243.80   $1,243.90