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 $240.41   9.417%   $263.0494   $263.05   $263.05   $263.00  
  Purchase #2 $96.61   7.574%   $103.9272   $103.93   $103.95   $103.90  
  Purchase #3 $141.60   8.285%   $153.3316   $153.33   $153.35   $153.30  
  Purchase #4 $61.57   12.184%   $69.0717   $69.07   $69.05   $69.10  
  Purchase #5 $249.43   9.320%   $272.6769   $272.68   $272.70   $272.70  
  Purchase #6 $134.65   12.821%   $151.9135   $151.91   $151.90   $151.90  
  Purchase #7 $46.95   9.273%   $51.3037   $51.30   $51.30   $51.30  
  7 purchase totals = $971.22       $1,065.2740   $1,065.27   $1,065.30   $1,065.20