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 $236.29   13.285%   $267.6811   $267.68   $267.70   $267.70  
  Purchase #2 $91.37   10.822%   $101.2581   $101.26   $101.25   $101.30  
  Purchase #3 $60.53   13.351%   $68.6114   $68.61   $68.60   $68.60  
  Purchase #4 $94.26   13.606%   $107.085   $107.09   $107.10   $107.10  
  Purchase #5 $125.57   8.759%   $136.5687   $136.57   $136.55   $136.60  
  Purchase #6 $43.37   3.405%   $44.8467   $44.85   $44.85   $44.80  
  Purchase #7 $108.61   12.353%   $122.0266   $122.03   $122.05   $122.00  
  7 purchase totals = $760.00       $848.0776   $848.09   $848.10   $848.10