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 $94.88   10.729%   $105.0597   $105.06   $105.05   $105.10  
  Purchase #2 $192.76   12.747%   $217.3311   $217.33   $217.35   $217.30  
  Purchase #3 $97.66   4.163%   $101.7256   $101.73   $101.75   $101.70  
  Purchase #4 $250.37   6.510%   $266.6691   $266.67   $266.65   $266.70  
  Purchase #5 $83.61   12.210%   $93.8188   $93.82   $93.80   $93.80  
  Purchase #6 $199.57   11.152%   $221.826   $221.83   $221.85   $221.80  
  Purchase #7 $187.36   12.332%   $210.4652   $210.47   $210.45   $210.50  
  7 purchase totals = $1,106.21       $1,216.8955   $1,216.91   $1,216.90   $1,216.90