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 $92.70   3.859%   $96.2773   $96.28   $96.30   $96.30  
  Purchase #2 $148.71   13.418%   $168.6639   $168.66   $168.65   $168.70  
  Purchase #3 $13.50   7.798%   $14.5527   $14.55   $14.55   $14.60  
  Purchase #4 $29.96   13.674%   $34.0567   $34.06   $34.05   $34.10  
  Purchase #5 $187.67   9.405%   $205.3204   $205.32   $205.30   $205.30  
  Purchase #6 $50.41   12.408%   $56.6649   $56.66   $56.65   $56.70  
  Purchase #7 $36.64   10.835%   $40.6099   $40.61   $40.60   $40.60  
  7 purchase totals = $559.59       $616.1458   $616.14   $616.10   $616.30