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 $28.96   12.613%   $32.6127   $32.61   $32.60   $32.60  
  Purchase #2 $60.39   10.592%   $66.7865   $66.79   $66.80   $66.80  
  Purchase #3 $212.36   5.792%   $224.6599   $224.66   $224.65   $224.70  
  Purchase #4 $15.69   9.343%   $17.1559   $17.16   $17.15   $17.20  
  Purchase #5 $191.75   8.502%   $208.0526   $208.05   $208.05   $208.10  
  Purchase #6 $120.39   6.161%   $127.8072   $127.81   $127.80   $127.80  
  Purchase #7 $152.75   13.524%   $173.4079   $173.41   $173.40   $173.40  
  7 purchase totals = $782.29       $850.4827   $850.49   $850.45   $850.60