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 $239.98   4.820%   $251.547   $251.55   $251.55   $251.50  
  Purchase #2 $157.99   3.189%   $163.0283   $163.03   $163.05   $163.00  
  Purchase #3 $174.64   10.662%   $193.2601   $193.26   $193.25   $193.30  
  Purchase #4 $221.30   11.169%   $246.017   $246.02   $246.00   $246.00  
  Purchase #5 $57.49   6.692%   $61.3372   $61.34   $61.35   $61.30  
  Purchase #6 $96.80   6.849%   $103.4298   $103.43   $103.45   $103.40  
  Purchase #7 $153.43   6.677%   $163.6745   $163.67   $163.65   $163.70  
  7 purchase totals = $1,101.63       $1,182.2939   $1,182.30   $1,182.30   $1,182.20