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 $61.55   7.335%   $66.0647   $66.06   $66.05   $66.10  
  Purchase #2 $143.87   13.687%   $163.5615   $163.56   $163.55   $163.60  
  Purchase #3 $87.69   5.626%   $92.6234   $92.62   $92.60   $92.60  
  Purchase #4 $159.35   9.627%   $174.6906   $174.69   $174.70   $174.70  
  Purchase #5 $151.36   10.465%   $167.1998   $167.20   $167.20   $167.20  
  Purchase #6 $16.76   4.866%   $17.5755   $17.58   $17.60   $17.60  
  Purchase #7 $220.65   10.538%   $243.9021   $243.90   $243.90   $243.90  
  7 purchase totals = $841.23       $925.6176   $925.61   $925.60   $925.70