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 $51.96   9.263%   $56.7731   $56.77   $56.75   $56.80  
  Purchase #2 $141.43   10.704%   $156.5687   $156.57   $156.55   $156.60  
  Purchase #3 $185.37   5.485%   $195.5375   $195.54   $195.55   $195.50  
  Purchase #4 $77.30   6.826%   $82.5765   $82.58   $82.60   $82.60  
  Purchase #5 $214.65   12.664%   $241.8333   $241.83   $241.85   $241.80  
  Purchase #6 $218.28   11.669%   $243.7511   $243.75   $243.75   $243.80  
  Purchase #7 $214.58   10.577%   $237.2761   $237.28   $237.30   $237.30  
  7 purchase totals = $1,103.57       $1,214.3163   $1,214.32   $1,214.35   $1,214.40