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 $63.71   6.659%   $67.9524   $67.95   $67.95   $68.00  
  Purchase #2 $137.92   12.533%   $155.2055   $155.21   $155.20   $155.20  
  Purchase #3 $76.51   10.774%   $84.7532   $84.75   $84.75   $84.80  
  Purchase #4 $153.50   8.149%   $166.0087   $166.01   $166.00   $166.00  
  Purchase #5 $44.78   7.616%   $48.1904   $48.19   $48.20   $48.20  
  Purchase #6 $142.46   7.860%   $153.6574   $153.66   $153.65   $153.70  
  Purchase #7 $226.45   10.662%   $250.5941   $250.59   $250.60   $250.60  
  7 purchase totals = $845.33       $926.3617   $926.36   $926.35   $926.50