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 $40.52   6.269%   $43.0602   $43.06   $43.05   $43.10  
  Purchase #2 $31.87   10.519%   $35.2224   $35.22   $35.20   $35.20  
  Purchase #3 $79.51   4.825%   $83.3464   $83.35   $83.35   $83.30  
  Purchase #4 $74.37   9.302%   $81.2879   $81.29   $81.30   $81.30  
  Purchase #5 $233.37   10.287%   $257.3768   $257.38   $257.40   $257.40  
  Purchase #6 $97.76   8.239%   $105.8144   $105.81   $105.80   $105.80  
  Purchase #7 $149.25   4.665%   $156.2125   $156.21   $156.20   $156.20  
  7 purchase totals = $706.65       $762.3206   $762.32   $762.30   $762.30