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 $125.59   6.698%   $134.002   $134.00   $134.00   $134.00  
  Purchase #2 $241.50   4.653%   $252.737   $252.74   $252.75   $252.70  
  Purchase #3 $8.87   4.195%   $9.2421   $9.24   $9.25   $9.20  
  Purchase #4 $98.55   8.203%   $106.6341   $106.63   $106.65   $106.60  
  Purchase #5 $79.66   3.685%   $82.5955   $82.60   $82.60   $82.60  
  Purchase #6 $89.82   10.373%   $99.137   $99.14   $99.15   $99.10  
  Purchase #7 $46.25   12.871%   $52.2028   $52.20   $52.20   $52.20  
  7 purchase totals = $690.24       $736.5505   $736.55   $736.60   $736.40