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 $248.25   8.670%   $269.7733   $269.77   $269.75   $269.80  
  Purchase #2 $221.56   8.622%   $240.6629   $240.66   $240.65   $240.70  
  Purchase #3 $198.83   5.386%   $209.539   $209.54   $209.55   $209.50  
  Purchase #4 $121.26   4.411%   $126.6088   $126.61   $126.60   $126.60  
  Purchase #5 $46.39   6.821%   $49.5543   $49.55   $49.55   $49.60  
  Purchase #6 $43.36   6.845%   $46.328   $46.33   $46.35   $46.30  
  Purchase #7 $52.33   5.165%   $55.0328   $55.03   $55.05   $55.00  
  7 purchase totals = $931.98       $997.4991   $997.49   $997.50   $997.50