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 $154.90   13.778%   $176.2421   $176.24   $176.25   $176.20  
  Purchase #2 $136.40   7.553%   $146.7023   $146.70   $146.70   $146.70  
  Purchase #3 $217.34   8.449%   $235.7031   $235.70   $235.70   $235.70  
  Purchase #4 $181.87   13.677%   $206.7444   $206.74   $206.75   $206.70  
  Purchase #5 $59.44   3.208%   $61.3468   $61.35   $61.35   $61.30  
  Purchase #6 $236.59   6.489%   $251.9423   $251.94   $251.95   $251.90  
  Purchase #7 $22.97   6.854%   $24.5444   $24.54   $24.55   $24.50  
  7 purchase totals = $1,009.51       $1,103.2254   $1,103.21   $1,103.25   $1,103.00