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 $214.63   11.842%   $240.0465   $240.05   $240.05   $240.00  
  Purchase #2 $126.61   5.401%   $133.4482   $133.45   $133.45   $133.40  
  Purchase #3 $96.60   8.112%   $104.4362   $104.44   $104.45   $104.40  
  Purchase #4 $73.66   8.585%   $79.9837   $79.98   $80.00   $80.00  
  Purchase #5 $97.32   7.630%   $104.7455   $104.75   $104.75   $104.70  
  Purchase #6 $152.52   13.871%   $173.676   $173.68   $173.70   $173.70  
  Purchase #7 $232.97   13.102%   $263.4937   $263.49   $263.50   $263.50  
  7 purchase totals = $994.31       $1,099.8298   $1,099.84   $1,099.90   $1,099.70