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 $238.82   11.437%   $266.1338   $266.13   $266.15   $266.10  
  Purchase #2 $113.93   3.248%   $117.6304   $117.63   $117.65   $117.60  
  Purchase #3 $121.41   3.789%   $126.0102   $126.01   $126.00   $126.00  
  Purchase #4 $7.94   6.157%   $8.4289   $8.43   $8.45   $8.40  
  Purchase #5 $206.96   4.822%   $216.9396   $216.94   $216.95   $216.90  
  Purchase #6 $16.80   7.378%   $18.0395   $18.04   $18.05   $18.00  
  Purchase #7 $10.45   13.193%   $11.8287   $11.83   $11.85   $11.80  
  7 purchase totals = $716.31       $765.0111   $765.01   $765.10   $764.80