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 $68.32   10.122%   $75.2354   $75.24   $75.25   $75.20  
  Purchase #2 $124.59   7.318%   $133.7075   $133.71   $133.70   $133.70  
  Purchase #3 $199.69   6.107%   $211.8851   $211.89   $211.90   $211.90  
  Purchase #4 $137.75   12.829%   $155.4219   $155.42   $155.40   $155.40  
  Purchase #5 $209.69   5.656%   $221.5501   $221.55   $221.55   $221.60  
  Purchase #6 $38.97   10.782%   $43.1717   $43.17   $43.15   $43.20  
  Purchase #7 $23.29   6.299%   $24.757   $24.76   $24.75   $24.80  
  7 purchase totals = $802.30       $865.7287   $865.74   $865.70   $865.80