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 $184.91   8.501%   $200.6292   $200.63   $200.65   $200.60  
  Purchase #2 $42.76   9.119%   $46.6593   $46.66   $46.65   $46.70  
  Purchase #3 $232.77   7.653%   $250.5839   $250.58   $250.60   $250.60  
  Purchase #4 $168.58   7.719%   $181.5927   $181.59   $181.60   $181.60  
  Purchase #5 $182.53   10.195%   $201.1389   $201.14   $201.15   $201.10  
  Purchase #6 $235.73   11.297%   $262.3604   $262.36   $262.35   $262.40  
  Purchase #7 $124.89   13.702%   $142.0024   $142.00   $142.00   $142.00  
  7 purchase totals = $1,172.17       $1,284.9668   $1,284.96   $1,285.00   $1,285.00