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 $65.92   4.359%   $68.7935   $68.79   $68.80   $68.80  
  Purchase #2 $152.85   9.641%   $167.5863   $167.59   $167.60   $167.60  
  Purchase #3 $86.58   8.456%   $93.9012   $93.90   $93.90   $93.90  
  Purchase #4 $76.74   12.807%   $86.5681   $86.57   $86.55   $86.60  
  Purchase #5 $185.65   12.374%   $208.6223   $208.62   $208.60   $208.60  
  Purchase #6 $117.64   8.868%   $128.0723   $128.07   $128.05   $128.10  
  Purchase #7 $69.83   3.326%   $72.1525   $72.15   $72.15   $72.20  
  7 purchase totals = $755.21       $825.6962   $825.69   $825.65   $825.80