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 $235.58   11.755%   $263.2724   $263.27   $263.25   $263.30  
  Purchase #2 $103.93   5.767%   $109.9236   $109.92   $109.90   $109.90  
  Purchase #3 $15.77   12.724%   $17.7766   $17.78   $17.80   $17.80  
  Purchase #4 $110.35   10.281%   $121.6951   $121.70   $121.70   $121.70  
  Purchase #5 $111.36   12.681%   $125.4816   $125.48   $125.50   $125.50  
  Purchase #6 $200.62   7.122%   $214.9082   $214.91   $214.90   $214.90  
  Purchase #7 $151.99   10.651%   $168.1785   $168.18   $168.20   $168.20  
  7 purchase totals = $929.60       $1,021.2360   $1,021.24   $1,021.25   $1,021.30