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 $94.27   11.841%   $105.4325   $105.43   $105.45   $105.40  
  Purchase #2 $37.38   5.122%   $39.2946   $39.29   $39.30   $39.30  
  Purchase #3 $22.45   13.710%   $25.5279   $25.53   $25.55   $25.50  
  Purchase #4 $188.46   7.305%   $202.227   $202.23   $202.25   $202.20  
  Purchase #5 $75.61   8.144%   $81.7677   $81.77   $81.75   $81.80  
  Purchase #6 $106.38   5.721%   $112.466   $112.47   $112.45   $112.50  
  Purchase #7 $184.77   4.600%   $193.2694   $193.27   $193.25   $193.30  
  7 purchase totals = $709.32       $759.9851   $759.99   $760.00   $760.00