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 $83.95   10.518%   $92.7799   $92.78   $92.80   $92.80  
  Purchase #2 $56.96   11.629%   $63.5839   $63.58   $63.60   $63.60  
  Purchase #3 $71.39   6.590%   $76.0946   $76.09   $76.10   $76.10  
  Purchase #4 $9.82   7.292%   $10.5361   $10.54   $10.55   $10.50  
  Purchase #5 $229.85   11.775%   $256.9148   $256.91   $256.90   $256.90  
  Purchase #6 $223.59   11.238%   $248.717   $248.72   $248.70   $248.70  
  Purchase #7 $192.67   5.187%   $202.6638   $202.66   $202.65   $202.70  
  7 purchase totals = $868.23       $951.2901   $951.28   $951.30   $951.30