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 $230.80   10.377%   $254.7501   $254.75   $254.75   $254.80  
  Purchase #2 $33.32   3.867%   $34.6085   $34.61   $34.60   $34.60  
  Purchase #3 $187.64   8.838%   $204.2236   $204.22   $204.20   $204.20  
  Purchase #4 $86.90   4.480%   $90.7931   $90.79   $90.80   $90.80  
  Purchase #5 $223.80   3.426%   $231.4674   $231.47   $231.45   $231.50  
  Purchase #6 $175.71   12.821%   $198.2378   $198.24   $198.25   $198.20  
  Purchase #7 $47.63   3.654%   $49.3704   $49.37   $49.35   $49.40  
  7 purchase totals = $985.80       $1,063.4509   $1,063.45   $1,063.40   $1,063.50