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 $94.83   11.856%   $106.073   $106.07   $106.05   $106.10  
  Purchase #2 $156.71   11.703%   $175.0498   $175.05   $175.05   $175.00  
  Purchase #3 $71.58   5.274%   $75.3551   $75.36   $75.35   $75.40  
  Purchase #4 $126.32   4.491%   $131.993   $131.99   $132.00   $132.00  
  Purchase #5 $214.26   13.613%   $243.4272   $243.43   $243.45   $243.40  
  Purchase #6 $182.36   12.565%   $205.2735   $205.27   $205.25   $205.30  
  Purchase #7 $157.32   7.242%   $168.7131   $168.71   $168.70   $168.70  
  7 purchase totals = $1,003.38       $1,105.8847   $1,105.88   $1,105.85   $1,105.90