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 $243.79   7.474%   $262.0109   $262.01   $262.00   $262.00  
  Purchase #2 $232.59   8.867%   $253.2138   $253.21   $253.20   $253.20  
  Purchase #3 $33.38   8.748%   $36.3001   $36.30   $36.30   $36.30  
  Purchase #4 $105.51   12.323%   $118.512   $118.51   $118.50   $118.50  
  Purchase #5 $11.39   8.551%   $12.364   $12.36   $12.35   $12.40  
  Purchase #6 $243.81   3.425%   $252.1605   $252.16   $252.15   $252.20  
  Purchase #7 $46.60   12.168%   $52.2703   $52.27   $52.25   $52.30  
  7 purchase totals = $917.07       $986.8316   $986.82   $986.75   $986.90