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 $124.98   13.253%   $141.5436   $141.54   $141.55   $141.50  
  Purchase #2 $241.96   11.352%   $269.4273   $269.43   $269.45   $269.40  
  Purchase #3 $92.71   4.277%   $96.6752   $96.68   $96.70   $96.70  
  Purchase #4 $104.29   3.306%   $107.7378   $107.74   $107.75   $107.70  
  Purchase #5 $108.27   9.222%   $118.2547   $118.25   $118.25   $118.30  
  Purchase #6 $118.81   13.249%   $134.5511   $134.55   $134.55   $134.60  
  Purchase #7 $27.99   9.697%   $30.7042   $30.70   $30.70   $30.70  
  7 purchase totals = $819.01       $898.8939   $898.89   $898.95   $898.90