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 $120.28   5.792%   $127.2466   $127.25   $127.25   $127.20  
  Purchase #2 $193.65   3.142%   $199.7345   $199.73   $199.75   $199.70  
  Purchase #3 $17.35   6.368%   $18.4548   $18.45   $18.45   $18.50  
  Purchase #4 $24.76   6.506%   $26.3709   $26.37   $26.35   $26.40  
  Purchase #5 $189.83   3.672%   $196.8006   $196.80   $196.80   $196.80  
  Purchase #6 $189.79   4.732%   $198.7709   $198.77   $198.75   $198.80  
  Purchase #7 $7.27   9.290%   $7.9454   $7.95   $7.95   $7.90  
  7 purchase totals = $742.93       $775.3237   $775.32   $775.30   $775.30