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 $43.85   13.689%   $49.8526   $49.85   $49.85   $49.90  
  Purchase #2 $187.84   10.569%   $207.6928   $207.69   $207.70   $207.70  
  Purchase #3 $237.96   12.735%   $268.2642   $268.26   $268.25   $268.30  
  Purchase #4 $94.66   3.298%   $97.7819   $97.78   $97.80   $97.80  
  Purchase #5 $160.56   9.530%   $175.8614   $175.86   $175.85   $175.90  
  Purchase #6 $220.86   10.800%   $244.7129   $244.71   $244.70   $244.70  
  Purchase #7 $191.78   3.298%   $198.1049   $198.10   $198.10   $198.10  
  7 purchase totals = $1,137.51       $1,242.2707   $1,242.25   $1,242.25   $1,242.40