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 $136.66   6.862%   $146.0376   $146.04   $146.05   $146.00  
  Purchase #2 $220.69   9.452%   $241.5496   $241.55   $241.55   $241.50  
  Purchase #3 $242.92   10.661%   $268.8177   $268.82   $268.80   $268.80  
  Purchase #4 $217.79   7.549%   $234.231   $234.23   $234.25   $234.20  
  Purchase #5 $114.33   12.476%   $128.5938   $128.59   $128.60   $128.60  
  Purchase #6 $197.65   9.681%   $216.7845   $216.78   $216.80   $216.80  
  Purchase #7 $86.83   10.657%   $96.0835   $96.08   $96.10   $96.10  
  7 purchase totals = $1,216.87       $1,332.0977   $1,332.09   $1,332.15   $1,332.00