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 $248.39   10.442%   $274.3269   $274.33   $274.35   $274.30  
  Purchase #2 $145.45   12.291%   $163.3273   $163.33   $163.35   $163.30  
  Purchase #3 $250.37   10.869%   $277.5827   $277.58   $277.60   $277.60  
  Purchase #4 $87.49   9.119%   $95.4682   $95.47   $95.45   $95.50  
  Purchase #5 $249.35   8.542%   $270.6495   $270.65   $270.65   $270.60  
  Purchase #6 $69.83   4.735%   $73.1365   $73.14   $73.15   $73.10  
  Purchase #7 $34.44   6.128%   $36.5505   $36.55   $36.55   $36.60  
  7 purchase totals = $1,085.32       $1,191.0416   $1,191.05   $1,191.10   $1,191.00