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 $59.42   6.541%   $63.3067   $63.31   $63.30   $63.30  
  Purchase #2 $219.89   5.771%   $232.5799   $232.58   $232.60   $232.60  
  Purchase #3 $25.64   10.797%   $28.4084   $28.41   $28.40   $28.40  
  Purchase #4 $163.68   10.645%   $181.1037   $181.10   $181.10   $181.10  
  Purchase #5 $242.79   4.857%   $254.5823   $254.58   $254.60   $254.60  
  Purchase #6 $30.81   11.625%   $34.3917   $34.39   $34.40   $34.40  
  Purchase #7 $245.41   6.746%   $261.9654   $261.97   $261.95   $262.00  
  7 purchase totals = $987.64       $1,056.3381   $1,056.34   $1,056.35   $1,056.40