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 $208.52   13.481%   $236.6306   $236.63   $236.65   $236.60  
  Purchase #2 $47.63   10.775%   $52.7621   $52.76   $52.75   $52.80  
  Purchase #3 $76.36   9.715%   $83.7784   $83.78   $83.80   $83.80  
  Purchase #4 $237.68   11.142%   $264.1623   $264.16   $264.15   $264.20  
  Purchase #5 $211.47   3.264%   $218.3724   $218.37   $218.35   $218.40  
  Purchase #6 $206.35   6.705%   $220.1858   $220.19   $220.20   $220.20  
  Purchase #7 $91.87   12.852%   $103.6771   $103.68   $103.70   $103.70  
  7 purchase totals = $1,079.88       $1,179.5687   $1,179.57   $1,179.60   $1,179.70