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 $250.43   13.680%   $284.6888   $284.69   $284.70   $284.70  
  Purchase #2 $181.28   8.219%   $196.1794   $196.18   $196.20   $196.20  
  Purchase #3 $239.65   6.398%   $254.9828   $254.98   $255.00   $255.00  
  Purchase #4 $57.48   3.465%   $59.4717   $59.47   $59.45   $59.50  
  Purchase #5 $81.61   6.769%   $87.1342   $87.13   $87.15   $87.10  
  Purchase #6 $238.33   11.204%   $265.0325   $265.03   $265.05   $265.00  
  Purchase #7 $26.37   8.572%   $28.6304   $28.63   $28.65   $28.60  
  7 purchase totals = $1,075.15       $1,176.1198   $1,176.11   $1,176.20   $1,176.10