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 $58.93   6.491%   $62.7551   $62.76   $62.75   $62.80  
  Purchase #2 $89.32   6.391%   $95.0284   $95.03   $95.05   $95.00  
  Purchase #3 $240.51   7.487%   $258.517   $258.52   $258.50   $258.50  
  Purchase #4 $211.97   4.517%   $221.5447   $221.54   $221.55   $221.50  
  Purchase #5 $42.61   11.416%   $47.4744   $47.47   $47.45   $47.50  
  Purchase #6 $68.67   6.516%   $73.1445   $73.14   $73.15   $73.10  
  Purchase #7 $89.87   4.271%   $93.7083   $93.71   $93.70   $93.70  
  7 purchase totals = $801.88       $852.1724   $852.17   $852.15   $852.10