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 $104.70   8.161%   $113.2446   $113.24   $113.25   $113.20  
  Purchase #2 $28.92   12.737%   $32.6035   $32.60   $32.60   $32.60  
  Purchase #3 $44.65   4.517%   $46.6668   $46.67   $46.65   $46.70  
  Purchase #4 $152.27   3.855%   $158.14   $158.14   $158.15   $158.10  
  Purchase #5 $208.50   13.588%   $236.831   $236.83   $236.85   $236.80  
  Purchase #6 $156.42   3.224%   $161.463   $161.46   $161.45   $161.50  
  Purchase #7 $84.89   13.464%   $96.3196   $96.32   $96.30   $96.30  
  7 purchase totals = $780.35       $845.2685   $845.26   $845.25   $845.20