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 $137.52   10.331%   $151.7272   $151.73   $151.75   $151.70  
  Purchase #2 $189.53   8.728%   $206.0722   $206.07   $206.05   $206.10  
  Purchase #3 $21.47   12.252%   $24.1005   $24.10   $24.10   $24.10  
  Purchase #4 $227.50   4.396%   $237.5009   $237.50   $237.50   $237.50  
  Purchase #5 $243.40   9.372%   $266.2114   $266.21   $266.20   $266.20  
  Purchase #6 $53.39   6.105%   $56.6495   $56.65   $56.65   $56.60  
  Purchase #7 $51.26   13.696%   $58.2806   $58.28   $58.30   $58.30  
  7 purchase totals = $924.07       $1,000.5423   $1,000.54   $1,000.55   $1,000.50