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 $87.94   5.522%   $92.796   $92.80   $92.80   $92.80  
  Purchase #2 $60.66   7.553%   $65.2416   $65.24   $65.25   $65.20  
  Purchase #3 $82.79   4.831%   $86.7896   $86.79   $86.80   $86.80  
  Purchase #4 $43.95   4.840%   $46.0772   $46.08   $46.10   $46.10  
  Purchase #5 $250.28   11.569%   $279.2349   $279.23   $279.25   $279.20  
  Purchase #6 $8.59   13.679%   $9.765   $9.77   $9.75   $9.80  
  Purchase #7 $92.58   3.191%   $95.5342   $95.53   $95.55   $95.50  
  7 purchase totals = $626.79       $675.4385   $675.44   $675.50   $675.40