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 $234.95   13.753%   $267.2627   $267.26   $267.25   $267.30  
  Purchase #2 $239.58   7.149%   $256.7076   $256.71   $256.70   $256.70  
  Purchase #3 $26.34   10.312%   $29.0562   $29.06   $29.05   $29.10  
  Purchase #4 $223.78   7.643%   $240.8835   $240.88   $240.90   $240.90  
  Purchase #5 $58.53   12.509%   $65.8515   $65.85   $65.85   $65.90  
  Purchase #6 $187.97   9.479%   $205.7877   $205.79   $205.80   $205.80  
  Purchase #7 $92.64   3.329%   $95.724   $95.72   $95.70   $95.70  
  7 purchase totals = $1,063.79       $1,161.2732   $1,161.27   $1,161.25   $1,161.40