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 $124.95   13.404%   $141.6983   $141.70   $141.70   $141.70  
  Purchase #2 $170.47   13.866%   $194.1074   $194.11   $194.10   $194.10  
  Purchase #3 $31.54   11.429%   $35.1447   $35.14   $35.15   $35.10  
  Purchase #4 $234.92   12.246%   $263.6883   $263.69   $263.70   $263.70  
  Purchase #5 $177.58   8.410%   $192.5145   $192.51   $192.50   $192.50  
  Purchase #6 $97.88   12.229%   $109.8497   $109.85   $109.85   $109.80  
  Purchase #7 $208.90   6.639%   $222.7689   $222.77   $222.75   $222.80  
  7 purchase totals = $1,046.24       $1,159.7718   $1,159.77   $1,159.75   $1,159.70