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 $234.50   3.460%   $242.6137   $242.61   $242.60   $242.60  
  Purchase #2 $176.74   10.523%   $195.3384   $195.34   $195.35   $195.30  
  Purchase #3 $134.37   6.593%   $143.229   $143.23   $143.25   $143.20  
  Purchase #4 $61.33   10.145%   $67.5519   $67.55   $67.55   $67.60  
  Purchase #5 $182.97   8.566%   $198.6432   $198.64   $198.65   $198.60  
  Purchase #6 $134.51   4.527%   $140.5993   $140.60   $140.60   $140.60  
  Purchase #7 $96.29   11.799%   $107.6513   $107.65   $107.65   $107.70  
  7 purchase totals = $1,020.71       $1,095.6268   $1,095.62   $1,095.65   $1,095.60