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 $58.76   7.619%   $63.2369   $63.24   $63.25   $63.20  
  Purchase #2 $229.69   11.330%   $255.7139   $255.71   $255.70   $255.70  
  Purchase #3 $208.52   8.212%   $225.6437   $225.64   $225.65   $225.60  
  Purchase #4 $129.77   9.298%   $141.836   $141.84   $141.85   $141.80  
  Purchase #5 $193.33   7.111%   $207.0777   $207.08   $207.10   $207.10  
  Purchase #6 $86.60   13.448%   $98.246   $98.25   $98.25   $98.20  
  Purchase #7 $92.39   11.704%   $103.2033   $103.20   $103.20   $103.20  
  7 purchase totals = $999.06       $1,094.9575   $1,094.96   $1,095.00   $1,094.80