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 $68.33   13.752%   $77.7267   $77.73   $77.75   $77.70  
  Purchase #2 $110.87   12.603%   $124.8429   $124.84   $124.85   $124.80  
  Purchase #3 $70.39   8.731%   $76.5358   $76.54   $76.55   $76.50  
  Purchase #4 $228.78   12.169%   $256.6202   $256.62   $256.60   $256.60  
  Purchase #5 $78.88   7.336%   $84.6666   $84.67   $84.65   $84.70  
  Purchase #6 $144.72   5.511%   $152.6955   $152.70   $152.70   $152.70  
  Purchase #7 $134.77   12.716%   $151.9074   $151.91   $151.90   $151.90  
  7 purchase totals = $836.74       $924.9951   $925.01   $925.00   $924.90