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 $229.86   5.804%   $243.2011   $243.20   $243.20   $243.20  
  Purchase #2 $208.30   11.631%   $232.5274   $232.53   $232.55   $232.50  
  Purchase #3 $53.79   12.627%   $60.5821   $60.58   $60.60   $60.60  
  Purchase #4 $211.99   9.673%   $232.4958   $232.50   $232.50   $232.50  
  Purchase #5 $11.45   11.469%   $12.7632   $12.76   $12.75   $12.80  
  Purchase #6 $68.51   13.625%   $77.8445   $77.84   $77.85   $77.80  
  Purchase #7 $69.40   5.282%   $73.0657   $73.07   $73.05   $73.10  
  7 purchase totals = $853.30       $932.4798   $932.48   $932.50   $932.50