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 $59.26   10.671%   $65.5836   $65.58   $65.60   $65.60  
  Purchase #2 $144.68   9.576%   $158.5346   $158.53   $158.55   $158.50  
  Purchase #3 $250.26   5.251%   $263.4012   $263.40   $263.40   $263.40  
  Purchase #4 $42.44   11.772%   $47.436   $47.44   $47.45   $47.40  
  Purchase #5 $215.96   7.506%   $232.17   $232.17   $232.15   $232.20  
  Purchase #6 $81.53   5.705%   $86.1813   $86.18   $86.20   $86.20  
  Purchase #7 $208.31   8.708%   $226.4496   $226.45   $226.45   $226.40  
  7 purchase totals = $1,002.44       $1,079.7563   $1,079.75   $1,079.80   $1,079.70