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 $193.83   5.346%   $204.1922   $204.19   $204.20   $204.20  
  Purchase #2 $68.67   6.834%   $73.3629   $73.36   $73.35   $73.40  
  Purchase #3 $135.68   5.804%   $143.5549   $143.55   $143.55   $143.60  
  Purchase #4 $87.76   8.401%   $95.1327   $95.13   $95.15   $95.10  
  Purchase #5 $191.32   12.249%   $214.7548   $214.75   $214.75   $214.80  
  Purchase #6 $171.46   9.491%   $187.7333   $187.73   $187.75   $187.70  
  Purchase #7 $57.74   13.825%   $65.7226   $65.72   $65.70   $65.70  
  7 purchase totals = $906.46       $984.4534   $984.43   $984.45   $984.50