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 $243.88   8.815%   $265.378   $265.38   $265.40   $265.40  
  Purchase #2 $73.42   5.419%   $77.3986   $77.40   $77.40   $77.40  
  Purchase #3 $185.69   4.366%   $193.7972   $193.80   $193.80   $193.80  
  Purchase #4 $58.67   11.550%   $65.4464   $65.45   $65.45   $65.40  
  Purchase #5 $81.71   13.731%   $92.9296   $92.93   $92.95   $92.90  
  Purchase #6 $189.34   12.768%   $213.5149   $213.51   $213.50   $213.50  
  Purchase #7 $130.64   13.376%   $148.1144   $148.11   $148.10   $148.10  
  7 purchase totals = $963.35       $1,056.5791   $1,056.58   $1,056.60   $1,056.50