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 $208.79   12.338%   $234.5505   $234.55   $234.55   $234.60  
  Purchase #2 $188.54   9.186%   $205.8593   $205.86   $205.85   $205.90  
  Purchase #3 $110.54   8.331%   $119.7491   $119.75   $119.75   $119.70  
  Purchase #4 $112.77   12.108%   $126.4242   $126.42   $126.40   $126.40  
  Purchase #5 $198.81   4.749%   $208.2515   $208.25   $208.25   $208.30  
  Purchase #6 $188.82   8.316%   $204.5223   $204.52   $204.50   $204.50  
  Purchase #7 $167.59   8.151%   $181.2503   $181.25   $181.25   $181.30  
  7 purchase totals = $1,175.86       $1,280.6072   $1,280.60   $1,280.55   $1,280.70