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 $126.44   7.689%   $136.162   $136.16   $136.15   $136.20  
  Purchase #2 $214.39   11.196%   $238.3931   $238.39   $238.40   $238.40  
  Purchase #3 $30.28   7.746%   $32.6255   $32.63   $32.65   $32.60  
  Purchase #4 $214.54   11.458%   $239.122   $239.12   $239.10   $239.10  
  Purchase #5 $154.70   9.304%   $169.0933   $169.09   $169.10   $169.10  
  Purchase #6 $91.53   5.758%   $96.8003   $96.80   $96.80   $96.80  
  Purchase #7 $237.36   7.326%   $254.749   $254.75   $254.75   $254.70  
  7 purchase totals = $1,069.24       $1,166.9452   $1,166.94   $1,166.95   $1,166.90