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 $106.68   7.526%   $114.7087   $114.71   $114.70   $114.70  
  Purchase #2 $59.68   9.299%   $65.2296   $65.23   $65.25   $65.20  
  Purchase #3 $131.62   12.287%   $147.7921   $147.79   $147.80   $147.80  
  Purchase #4 $195.37   5.205%   $205.539   $205.54   $205.55   $205.50  
  Purchase #5 $65.72   6.414%   $69.9353   $69.94   $69.95   $69.90  
  Purchase #6 $67.47   6.313%   $71.7294   $71.73   $71.75   $71.70  
  Purchase #7 $109.69   7.625%   $118.0539   $118.05   $118.05   $118.10  
  7 purchase totals = $736.23       $792.9880   $792.99   $793.05   $792.90