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 $165.87   5.564%   $175.099   $175.10   $175.10   $175.10  
  Purchase #2 $176.99   5.602%   $186.905   $186.91   $186.90   $186.90  
  Purchase #3 $110.55   3.383%   $114.2899   $114.29   $114.30   $114.30  
  Purchase #4 $158.30   7.739%   $170.5508   $170.55   $170.55   $170.60  
  Purchase #5 $12.72   8.490%   $13.7999   $13.80   $13.80   $13.80  
  Purchase #6 $146.32   13.611%   $166.2356   $166.24   $166.25   $166.20  
  Purchase #7 $191.75   4.188%   $199.7805   $199.78   $199.80   $199.80  
  7 purchase totals = $962.50       $1,026.6607   $1,026.67   $1,026.70   $1,026.70