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 $247.83   7.141%   $265.5275   $265.53   $265.55   $265.50  
  Purchase #2 $64.30   11.102%   $71.4386   $71.44   $71.45   $71.40  
  Purchase #3 $217.46   6.717%   $232.0668   $232.07   $232.05   $232.10  
  Purchase #4 $96.53   7.120%   $103.4029   $103.40   $103.40   $103.40  
  Purchase #5 $126.34   8.484%   $137.0587   $137.06   $137.05   $137.10  
  Purchase #6 $33.74   4.821%   $35.3666   $35.37   $35.35   $35.40  
  Purchase #7 $47.58   9.270%   $51.9907   $51.99   $52.00   $52.00  
  7 purchase totals = $833.78       $896.8518   $896.86   $896.85   $896.90